Billy Chan

Chapter 99 - Question Revision

Fri, 10 May 2019 00:00:00 +0000

Spread Spectrum

Spread-spectrum is designed to trade bandwidth efficiency for reliability, integrity, and security
FHSS
- Frequency Hopping Spread Spectrum
- Spectrum is divided into many subchannels
- two communicating systems hop on same frequency
DSSS
- Direct Sequence spread spectrum
  - stations are assigned orthogonal codes
  - use these code for transmission
  - other stations transmissions appears an noise

ARQ

Automatic Repeat reQuest
Reactive protocol
control protocols for transmission of data over noisy or unreliable communication network.
Use ACK and timeouts to acheive reliable data transmission
Stop-and-wait ARQ, Go-Back-N ARQ

Aloha VS slotted Aloha

Aloha
- a terminal transmits whenever the user data is ready
- if the sender finds that the packet get collided
  - it waits for a random period of time
  - send the packet again
- Throughput : $S_{pure} = Ge^{-2G}$
Slot-Aloha
- time is slotted
- length on the slot is the time to transmit a packet
- node starts transmission in the beginning of the slots only
- if collision occurs
  - sender waits for a random number of slots
  - transmit Packets agains
- Throughput: $S_{slotted} = Ge^{-G}$

Why does IEEE standardize only two lower layers for WLANs

only standardize PHY and MAC lyaer
Interfaces to higher layer is the same as those in iEEE 80.2x standards
The upper layers is still the same as normal LAN
what the different is the medium for tranmission , it is in wireless now.

BEB works in IEEE 802.11 WLAN.

Binary Exponential Backoff
When multiple entities attempt to gain access to a shared resource, only one of them will succeed.
Those who fail wait til the resoure becomes available then retry.
Binary Exponential Backoff (BEB) is an algorithm to determine how long entities should backoff before they retry.
With every unsuccessful attempt, the maximum backoff interval is doubled.
BEB prevents congestion and reduces the probability of entities requesting access at the same time,

Why RTS-CTS needed

- to solve hidden terminal problem

hidden terminal problem occurs when a node can communicate with a wireless access point (AP), but cannot directly communicate with other nodes that are communicating with that AP.
RTS-CTS
- the senders A sends RTS to receiver B
- once the receiver B get RTS, it starts to send CTS to all other terminals, indicating that sender A is going to communicate with receiver B. After the this handshake, they can start send data.

Network allocation vector

Shared Medium Access
- Carrier Sensing
  - Virtual Carrier Sensing
    - provided by the Network Allocation Vector (NAV)
    - NAV Indicates how long the medium is reserved
    - NAV is set acccrdoing to fields (Duration ) indicated in most frames
It is a virtual carrier sensing mechanism.
The station listens to duration field to set their NAV
It is a indicator for a station on how long it must defer from accessing the medium

ESS and Infrastruture BSS difference

Basic Service Set (BSS) : a set of stations communicating with each other

Extended Service Set (ESS): linking BSS using backbone network

Infrastructure BSS (Infracstruture mode)

Terminals communicate via AP
centralized

Extended Service Set (ESS):

provide larger service areas
does not specify pariticular technology
requires backbone to provide a specific set of service

Bluetooth topology

Piconet
- master and slaves architecture
- maximum up to 7 slaves
scatternet
- a group of piconet

Main Appilcation of ZigBee

Low Data-rate radio services
- Remote control,
- Joystick
- Personal Health care
- sensors

ZigBee Mesh Topology

MIssion of 3gpp

The 3rd Generation Partnership Project (3GPP)
developing globally acceptable specifications for third generation (3G) mobile systems.

shortcomings of CSMA/CD in wireless networks

collisions in wirerless channels are harder to detect
colisions leads to usage of bandwidth which is scarce

Which layers IEEE 802.11 specify in their standards? Why?

only standardize PHY and MAC lyaer
Interfaces to higher layer is the same as those in iEEE 802.x standards
The upper layers is still the same as normal LAN
what the different is the medium for tranmission , it is in wireless now.

What are two principle operation modes of 802.11a/b/g/n systems?

ad-hoc mode
infrastructure mode

Briefly explain evolution of air interface technology from GSM towards LTE.

GSM

TDMA and CDMA
FSK digital modulation

GPRS

EDGE

Why is ad-hoc networking useful in militaristic applications?

Chapter 14 - Public Protection and Disaster Relief Communications

Fri, 10 May 2019 00:00:00 +0000

Public Protection and Disaster Relief Communications

Definition

PPDR communications can be distinguished in those
- used by agencies and organizations responsible for dealing with
  - maintenance of law and order
  - protection of life and property , and emergency situations
- and in those used by agencies and organisations dealing with
  - a serious disruption of the functioning of society,
  - posing a significant, widespread threat to human life, health ,
  - property or the environment
- whether caused by
  - accident, human activity and ,
- whether developing suddenly or as a result of complex, long term processes

Users and types communication

Emergency response as multi-agent system
- Public safety agency should be always (24/7) ready for emergency response
- A multi-agent system is a system composed of multiple interacting intelligent agents.
- Rescue teams are in fact multi-agent systems where coordination is critical
  - to improve coordination such missions often rely on coordination centers that needs to be provided information in real-time;
  - the more information about the context of a mission is provided the more precise/efficient coordination is.
- Communication technologies is a significant factor of multi-agent systems’ performance
PPDR USERS
Regular Police
Fire Brigades
Emergency Medical Services (EMS)
Part-time Fire
Special police Functions
EMS civilian support
Police Civilian support
Fire civilian Support
Genreal Government Personnel
Types of communication
- human-to-human
- humah-to-machine
- machine-to-machine

Application and services

PPDR application
PPDR application 2
PPDR Broadband
Capabilities provided under Localized Communication Services

Obejctives according to ITU

Objective
to support the integration of voice, data, video and image communications as part of a multimedia capability;
to provide additional level(s) of priority, availability and layered security associated with the source, destination and type of information carried over the communication channels used by various PPDR applications and operations;
to provide each PPDR agency and organization with user authentication (e.g. public key cryptography) among PPDR agencies and organizations and for their devices prior to granting access to their applications or network resources;
to support operation in extreme or adverse environments (high mobility, heat, cold, dust, rain, water, noise, shock, vibration, extreme temperature, and extreme electromagnetics, etc.);
to support robust equipment (e.g. hardware, software, operational and maintenance aspects, long battery life). Equipment (handheld or transportable) that functions while the user is in motion is also required. Equipment may also require unique accessories, which could include special microphones;
to accommodate the use of repeaters for covering long distances between terminals and base stations in rural and remote areas and also for intensive on- scene localized areas;
to provide fast call set-up, one-touch broadcasting (PTT to group) and group call features;
to provide for emergency calls, one-touch emergency alert (emphasizing that this function is used in life threatening situations and should receive the highest level of priority), emergency voice PTTs, and emergency data PTTs (e.g. sending images, real-time video) during PPDR events;
to support information pull, push and subscription with prioritization;
to provide for strong multi-national/multi-agency technical interoperability over multi-network and device technologies in a seamless fashion
to provide Localized Communication Services (LCS), Relayed Device Mode Communications (RDM) , Direct Mode Operation (DMO);
to provide for the ability of PPDR communication systems to interface with other dedicated PPDR and/or commercial systems;
to be scalable in order to suit small and large agencies, without sacrificing the ability to interoperate;
to provide for quick deployment of temporary infrastructure and services as well as recovery from failure;
to support continuous use of basic PPDR services in case of infrastructure collapse or failure, e.g. loss of backhaul link between base station and core network;
to support the need for high level of security without compromising the response time;
to provide audio quality that ensures the listener is able to understand without repetition, identify the speaker, detect stress in a speaker’s voice, and hear background sounds without interfering with the primary voice communications.
Low Latency – very short call set up times (< 500 ms) and very limited end to end voice/data transmission delay (< 1 s).

Spectrum requriements

How to calculate for it
- Determine busy hour call attempts per PDDR user for each service in each environment
- Determine effective call/session duration
- Determine activity factor
- Calculate busy hour traffic per PPDR user
- Calculate offered traffic/cell for each service in each environment

Unique PPDR requirement
- Blocking = less than 1%
- Modularity= ~20 channels per cell per network
- Frequency reuse cell format
  - 12 for like power mobile or personal stations
  - 21 for mixture of high/low power mobile and personal stations.
- Determine number of service channels needed for each service in each “service” environment (NB, WB, BB).

Existing and future PPDR communication

Exisiting PPDR communication
- EU(380-400Mhz)
- The network deployment and relevant infrastructure is usually built for nationwide coverage and is owned by state agencies that permit network utilisation among public protection and disaster relief (public) organisations.
- These networks satisfy the security and reliability requirements.
- However, they can support a limited number of multimedia services.
Metrics of interest
- mean throughput per node
- fraction of time when at least one node is disconnected
- mean number of disconnected nodes

Conclusion

Emerging PPDR applications utilize heavy-traffic services, which can not be served by existing PPDR communication systems
Millimeter wave technologies may address wireless demands of heavy traffic applications, however, the reliability of mmW communication doesn’t satisfy the reliability requirements
The reliability of mmW communication can be enhanced by using mesh technology and AI
Development of technologies which improve the reliability of mmW is a relevant research challenge

Chapter 13 - Vehicular and Aerial Communication

Fri, 10 May 2019 00:00:00 +0000

Vehicular and Aerial Communication

Networks in 5G era and Beyond

The “Big Three” 5G technologies
- Ultra-densification
  - Leads to gross over-provisioning and more complex interference management
  - requires massive investment by mobile operators
- mmWave radios
- Massive MIMO

Emerging Research Vision Beyond 5G (B5G)

High-bandwidth
Large number
Very realiable

Intelligent connected and moving machines
- Massive mobile AR/VR/MR galsses
- Very large fleets of autonomous vehicles
- Cooperating drone swarms
- Collabortive moving robots

Research Challenges Beyond 5G

Access supply has been well-studied in the past
- but implication of user demand remain largely unexplored
Rethink wireless system design and content delivery for better matching the irregular user demand with the network access suplly in 5G systems
Proposed solution
- dynamic and mobile network infrastructures that intelligently leverage provisional and personal radio access equipment
  - Offer truly flexible and on-demand network architecture by involving operator- and user-owned connected machines without the associated high costs
  - Employ mobile base stations equipped with high-rate (e.g., mmWave) radio access capabilities
  - Leverage multi-radio uplink, downlink, direct device-to-device (D2D) links, as well as vehicle- and drone-assisted access

Expected Impact

Breakthrough goal
- reliable people-aware connectivity where space-time supply and demand may be shaped opportunistically
  - User-owned machines (high-end wearables, cars, drones, etc.)
  - take a more active role in 5G+ service provisioning (especially in partial coverage situations
    - Functional disparity between the network and the user equipment is rapidly becoming blurred
Theoretical benefits
- Orders of magnitude better network capacity scaling
  - Number of base stations: K
  - Min number of antennas : n
  - Avaliable bandwidth : W
  - Network capacity = $K \times n \times W \times log(SNR)$
Practical benefits
- clearly noticeable more stable and smoother user connectivity experience
- This research accentuates the importance of people as an integral component of beyond-5G system infrastructure with multiple impacts in industry, education, and community outreach

Chapter 12 - Ad hoc networks

Fri, 10 May 2019 00:00:00 +0000

Ad hoc networks

Cellular and ad-hoc wireless networks

Cellular networks	Ad-hoc wireless network
Fixed infrastructure	No infrastructure
Single-hop wireless links	Multi-hop wireless links
Guaranteed CBR bandwidth (voice traffic)	Shared radio channel (data traffic)
Initially, circuit-switched	Initially, packet-switched
High cost and time of deployment	Very quick and cost-effective
Reuse of frequency via channel reuse	Dynamic frequency sharing
Bandwidth reservation is achieved easily	Complex MAC layer
Nowadays applications: civilian, commercial	Nowadays applications: military, rescue
High cost of network maintenance	Maintenance operations are built-in
Low complexity of mobile devices	Intelligent mobile devices are required
Widely deployed, evolves	Still under development in commercial sector

Application of ad-hoc wireless network

applications
- military applications
- collaborative and distributed computing
- emergency and rescue operations
- mesh networks
- wireless sensor networks
- hybrid cellular / ad-hoc wireless networks
why ?
- quick depolyment
- inexpensive deployment and operation

Technical challenges

Medium Access Scheme

MAC usded for shared use of the transmission medium
performance depends on MAC protocol
chanllenges
- distribution operation
- maximum throughput
- minimum access delay
- fairness
- real-time trafiic support
- power control capabilities
- use of directional antennas
- hidden/exposed terminal problems

Routing

responsible for
- determining a feasible path
- discovering, storing, and exchanging routing information
- gathering information about a path breaks and updating route information accordingly
Challenges
- Mobility
- Bandwidth constraints
- Resource constraints
- Errorneous transmission medium
- Location-dependent contention
requirements on a routing protocol in ad-hoc networks
- minimum route acquisition delay
- Quick route configuration
- loop-free
- distributed routing
- low overhead
- scalabiltiy
- privacy
- support for time-sensitive traffic

Multicasting

Multicasting is an important feature in wireless ad-hoc networks:
- search and rescue operations: distribution of commands
- military applications: distribution of command
Why not to adapt something from fixed networks (CBT, PIM, DVMRP)
- core base trees (CBT), distance vector multicast routing protocol (DVMRP), etc.
- mobility of nodes changes the topology of the network! Trees are unstable!
There are following challenges in ad-hoc environment for multicasting:
- Fast recovery;
- Control overhead;
- Efficient group management;
- Scalability;
- Security.

Transport Layer Protocol

Major function of connection-based transport layer protocol:
- setting up and maintaining end-to-end connection
- reliable end-to-end delivery of data packets
- flow control
- congestion control
Why not to go with UDP
- does not perform flow and congestion control and reliable end-to-end transfer;
Performance degradation stems from
- high error rate
- frequent path breaks
- presence of ‘old’ routing information
- network partitioning

Quality of Service provisioning

QoS
- traffic performance in the network
- service support performance
- service operability performance
- service security performance
To satisfy QoS
- use values of traffic engineering variables that constitute the so-called Grade of Service (GoS)
Provision of QoS requires:
- negotiation between the host and a network
- resource reservation schemes
- priority scheduling
- call admission control

Self-organization

Self-organization is the main attractive property of ad-hoc networks.
To perform self-organization the following things are required:
- neighbour discovery
  - first phase when a node switches on;
  - a node should gather network information (transmission of reception of discovery packets).
- topology organization
  - every nodes gathers information about the entire network (a part of);
  - construct and maintain the network topology.
- topology reorganization
  - when links break, nodes switch off etc
  - requires periodic or aperiodic exchange of topology information.

Security

Ad hoc are more vlunerable to attacks because
- lack of central coordination
- shared wireless medium
Two types of attacks
- passive attacks
  - malicious nodes attempt to obtain information relayed in the network;
  - no damage to operation of the network, just capture if information
- active attacks
  - external attacks: attacks executed by nodes outside the network;
  - internal attacks: attacks executed by nodes belonging to the same network.
Denial of Service
Resource consumption
- Energy Depletion
  - to deplete the power of the node relaying the traffic through them.
- Buffer overflow
  - fill the routing table with ’bad’ entries to consume the buffer space of the target node.
Host impersonalization
Infomration disclosure
Interference

Addressing and service discovery

Addresses
- Global unique address
- autoconfiguration of address
- Duplicate address detection mechanism
Meaningful features for ad-hoc network
- automatic service advertisement mechanism
  - should allow to identify the current location of the service
  - it is not possible to assume static service locations in ad hoc networks.
- integration of service discovery protocols and routing protocols
  - may allow to easily find the necessary service in a networ
  - may violate the traditional design objectives of the routing protocol

Energy management

can be done
shaping the energy discharge pattern
use routes with minimal total energy consumption
use special task scheduling schemes
proper handling the processor and interface devices
can be achieved by
- Transmission power management
- Battery energy management
- Processor power management
- Interface power management

Scalability

Testbeds and operational ad hoc networks made so far:
- contain only a limited number of nodes
- may not be good examples of ad hoc performance
What we may expect in real implementations
- performance of ad-hoc network degrades drastically with the increase of the number of nodes
- one may expect commercial realization of, at least, thousands of nodes

Deployment

Low cost : no cables, no configuration, no maintenance
Incremental : functioning starts immediately after minimum configuration is done
short time : no cables, no configuration, no maintenance
reconfigurability : no cables, no configuration, no maintenance

Example : data-link/network/transport

Data-link layer MACA

MACA:
- stands for MAC protocol for ad hoc networks.
major facts
- contention-based without reservation and scheduling
- MACA was prposed as an extension for CSMA/CA protocol
- was further extended and adopted for IEEE 802.11
CSMA
- the sender sense the channel for the carrier signal;
- if the carrier is present it retries to sense the channel after some time (exp. back-off);
- if not, the sender transmits a packet
Shortcoming for CSMA/CA
- hidden terminal problem leading to frequent collisions;
- exposed terminal problem leading to worse bandwidth utilization

MACA avoids hidden and exposed terminal problems using the RTS-CTS.

RTS and CTS packets carry the expected duration of transmission;
a node near the sender
that hearing RTS do not transmit for a time to receive CTS;
a node near the receiver
- after hearing CTS differs its transmission
if the neighbor hears the RTS only
- it is free to transmit

Network layer: Location Aided routing (LAR)

use the location information
reactive protocol
Two zones
- Expected Zone
  - a geographical zone in which the location of the terminal is predicted based on:
    - location of the terminal in the past
    - mobility information of the terminal
- Request Zone
  - a geographical zone within which control packets are allowed to propagate
    - area is determined by the sender of the data packet
    - control packets are forwarded by node within a RequestZone only
    - if the node is not found using the first RequestZone, the size of RequestZone is increased.
Nodes decide whether to forward or discard packets based on two algorithms:
- LAR type 1
- LAR type 2

Transport-layer protocols: Split TCP

TCP major problems
- degradation of throughput with increase of path length
- unfairness among TCP flows
split-tcp provides the solution by splitting the TCP functionality into two part
- congestion control
  - local phenomenon due to high contention for resources
- end-to-reliability
  - end-to-end phenomenon

Split TCP:

splits the connection into a set of concatenated TCP connections
proxy node
- terminating the connection from the sender/precessor proxy node;
- setting up a connection with receiver/successor node.
- are chosen using the distributed algorithm
  - packet traversed n hops - behave as a proxy
Transmission control at the TCP sender window is split
- end-to-end CW
  - updated according to arrival of end-to-end ACKs
- local CW: (local CW ≤ end-to-end CW)
  - updated according to arrival of local ACKs (LACKs) from the next node.
Proxy node behaves
- it maintains local CW governing transmission in a segment;
- when packet arrives from predecessor the LACK is sent back;
- arrived packet is buffered;
- the buffered packet is forwarded to the next node.

Chapter 11 - WPANWBANs:Bluetooth and BLE

Fri, 10 May 2019 00:00:00 +0000

WPANWBANs:Bluetooth and BLE

PAN/BAN

IEEE 802.15

Discussed in Chapter10

BAN/PAN technical challenges and design issues

Technical challenges

Problems	Detail
Address is not a physical location	The station is not always stationary. The address does not give an information about location
Dynamically changed topology	The network connectivity is partial at times
Medium boundaries are soft	The communication range cannot be determined precisely.
Erroneous medium	BER in wireless network is about 10^-4compared to 10^-9 in fixed networks
Hidden terminal problem	Some nodes should (not) be allowed to communicate at a certain time

Design Issues

Ceriteria to be meet	Detail
Operational simplicity: BAN/PAN	Mobile use MUST be able to quickly set up and access network services in a SIMPLE manner
Power efficienct operation: BAN/PAN	The main resource of MT is the power: power saving features
Licence-free operation: PAN	Lost cost installation is required for widespread usage, e.g., ISM band
Tolerance to interference: BAN/PAN	There are a lot of technologies operating in ISM band causing interference between them.
Security: PAN	PAN is vulnerable to different attacks
Compatibility: BAN/PAN	Compatibility with other technologies and applications is required for a commercial success.

Bluetooth general description

What bluetooth appears?

the need for personal services to communicate directly without infrastructure
PAN/BAN paradigms have appeared
Bluetooth is the most successful standard for BAN/PAN

Bluetooth specifications

Basic structure
- Core specifications : DL and PHY PROTOCOLS
- Profiles : applications
Functions performed by the stack
- locating/connecting devices,exchanging data
Functions Logically divided into three groups
- transport protocol group
  - RF: radio and antenna;
  - baseband sublayer
  - ling mangager, logical link control and adaptation sublayers
  - host controller interface
- middleware protocol group
  - RFCOMM, SDP, TCS
- application group
  - profiles

Network Topologies

Transport Protocol Group(TPG)

locating services: allows devices to locate each other
creating, configuring, and managing wireless link
TPG aims
- low power consumption
- simplicity of operation
- low cost of the communicating entity
Three genreral choices were made for bluetooth
- master-slave architecture (simplicity)
- frequency hopping communication (tolerence to interference)
- gateway-based large newtorking (extensions)

Piconet

consists of the master and slaves, initiator of the formation: master;
can have up to seven active(!!!) slaves at any time
each active slave of the piconet is a unique active member address BD_ADDR.

Scatternets

Piconet may operate spatially
- piconets can operate in the same area in the same time
- each piconet is characterized by a unique master;
- piconets hop independently with its own hopping sequences.
- with more piconets added, probability of collision increases (frequency hopping).
Only a few active devices in Piconet
- Bluetooth unit may operate as a slave in different piconets
- Bluetooth unit may operate as a master in only one piconet!

DEFINITION: A group of piconets between which connections exist is called a scatternet.

Transport Protocol Group

It deals with
- PHY layer
- data-link layer
Bluetooth radio
- in ISM frequency
- a variance of frequency modulation, GFSK
- 64Kbps voice channel
- asynchronous data channel with peak rate of 1Mbps
- FHSS(Frequency-hopping spread spectrum) operating over the set of m = 79 channels each of width of 1MHz;
- hops are made across all channels starting at 2.402GHz and stopping at 2.480GHz;
- the transmit power of 1mW, extension to 100mW;
- the nominal link range is up to 10m (1mW), can be extended to 100m (100mW).

Baseband sublayer

functions
- hop selection
- connection setup
- medium access control
Creating and maintaining piconets
- the address of a device
  - three part 48 bit address
    - lower address part (LAP): used in piconet ID, error, security checking
    - reamining two parts are addresses assigned by manufacturer
- the clock associated with a device
  - native clock : 28 bit clock
  - 3200 times persecond (interval is 312.5 us)
  - 3200 is twice the hopping rate (1600 hops/s)

Organization of the communication channel

Basic
- the channel is divided into time slots of 625 μs
- TDD (Time-division Duplex )scheme is used where master and slave alternatively transmits
- packet transmission is aligned with the beginning of the slot
- slots are numbered according to the clock of the master
- master starts its transmission in even-numbered slots, slave in odd-numbered slots only
- slave is allowed to transmit only if in the preceding slot it received a packet from the master

State operations in Bluetooth

Selection of frequency hopping sequence

Hopping sequence: FSM
- clock value
- address
Clock and address are different in different modes
- Connected State:
  - The clock value of unknown
  - the address of the device is known
- Inquiry State
  - address input to FSM is a inquiry address
  - at the time of inquiry, no device has information about the hopping sequence
- Paging State
  - The address of the paged device is entered in FSM

Inquiry State

Essential state for bluetooth
- any device which is initially in the standby state enters the inquiry state
- to collect information about other Bluetooth devices in its neighborhood
  - infomration includes address and clock value of the master
The Inquiry proceeds as follows
- master sends an inquiry packet on the inquiry hop sequence of frequencies
  - the common address is fed to the FSM
- a device that wants to be discovered enters the inquiry state and listens for these packets
- when inquiry message is received, responses with packet containing the device address.

Page State

Why to enter and from which state
- to invite other devices to join a piconet
- to inquiry operation precedes this state
Three substates
- Page sub-state(master)
  - the master estimates the slave clock value
  - determines the hop sequence where the slave might be listening in the page scan mode
  - transmits the page message in preceding, estimated and following hop sequences
- Page scan sub-state(slave)
  - slave listens the channel for a page message
  - upon receiving the page message the salve enters the salve page response sub-state
  - slave sends page response message
- Page response sub-state
  - the master informs the salve about its clock and address
  - the salve calculates an offset to sychronize with the master clock

Connected State

Packet-based communication

Access code
- contains the address of the piconet master
- all packets exchanged on the channel are identified by the master’s identity
Header
- three bit active slave number
  - the maximum number of slaves in the piconet is 7;
- a one bit ACK/NACK field
  - to retransmit erroneously received frames;
- four bit packet type field:
  - to distinguish between payload types
- eight bit header error check
  - to detect errors in the header
Payload
Depending on the payload size ONE, THREE, OR FIVE slots can be used for packet
Above
- single slots are used to transmits packets
- frequencies are F(k), F(k+2), F(k+4), F(k+6) for transmission slots.
Middle
- two slots are used to transmit a first packet
- requency F(k+4), not F(k+3) is used for transmitting a packet
Links in a piconet
- asynchronous connectionless link (ACL)
  - default link that exists once the connection established
  - whenever a master would like to communicate, it does so
  - slave can only respond after the master’s transmission
- syncrhonous connection-oriented link(SCO)
  - SCO link is a symmetric between master and a slave with reserved bandwidth
    - reserved bandwidth: just reserved time slots at regular intervals;
  - why: high-priority and time-bound information such as video and audio.
Communication in a piconet
- only between master and its slaves
- is not possible between slaves
- master does not route packets of its slaves

Link Management Protocol

Functions
- setting and maintaining the properties of the Bluetooth link
- power management
- security management
Power Management
- Active mode
  - actively participates in the piconet
- Sniff mode
  - listen only certain slots
  - master commands the source to go to this mode
- Hold mode
  - slave temporarily does not support ACL packets on the channel
  - capacity is made available for paging, inquiring, or attending another piconets
- Park Mode
  - very low-power mode allowing master to have more than 7 slaves
  - slave is given an eight bit parked member address, remains synchronized, no active address
  - a message to the parked station is sent over broadcast channel
Security
- key management : to share and distribute keys
- authentication : to know the communicating entity
- encryption: performed for packet payloads
Error detection and correction
- detect : checksum is added to a packet
- correct: FEC with two rates (1/2,1/3): flexible for payload, strict (1/3) for header;
- correct: ARQ with ACKs and NACKs

Host controller interface

Functionality
- interface layer between the layers above LMP and lower layers
- provides access to Bluetooth hardware capabilities

Logical Link control and adaptation protocol (L2CAP)

Functionality
- abstraction of higher layer protocols via multiplexing of protocols
- segments and resembles packets to combot BER

Middleware protocols

provides standard interface to applications
- Service discovery protocol(SDP)
  - Fully automatic of request-response type
- RFCOMM
  - virtual serial port, any application that use serial port can work seamlessly
- IrDA interoperability protocols
  - IrDA object exchange (IrOBEX) used for exchanging objects between two devices;
  - Infrared Mobile Communication protocol (IrMC) used for synchronization
- Telephony control specification (TCS)
  - audio signal are carried out over SCO at 64kbps
  - defines
    - call control
    - group management
    - connectionless TCS

Bluetooth Profiles

What and Why
- provides standard to implement a specifc user function
- to allow interoperability between different Bluetooth implementations
13 profiles are calssifiled into
- Generic Profiles
- Telephony Profiles
- Networking Profiles
- Serial and object exchange profiles

Advantage and shortcoming of BT

Advantage	Shortcomings
fill the gap in networking on scales shorter than WLAN	Does not provide support for routing
exceptionally well standardized	No support of handover
	Master is a bottleneck
	Bluetooth has operates in ISM band like 802.11b WLAN
	Complexity grows

Bluetooth low energy(BLE)

why BLE

bluetooth is doing extremely well
bluetooth is good for industry
very robust to interference , frequency hopping
compete with Zigbee

Definiition and benefits

definition
- open, low energy and short range wireless technology
benefits (good for small, discrete data transfers)
- low power consumption
- small size
- connectivity to mobile phone
- low cost, robust, efficient
- multi-vendor interoperability
- global availability, license free
temperature, time, pressure, speed sensing
2mAh per day

Constraints

Imposed constraints
- reuse as much Bluetooth RF as possible
  - only need 60% RF silicon area compared to Bluetooth
  - can use the same antenna as Bluetooth
  - can TDM with BT
- reuse as much BluetoothL2CAP as possible
- reuse as much Bluetooth hHCI as possible
  - same HCI physicial interfaces
  - same HCI packet formats
  - same HCI drivers in OS
Design Goals
- lowest possible power operation
  - turning radio off for as much of the time as possible
  - reducing the complexity of a single mode device to almost nothing
    - reduced memeory requirement
      - reduced leackage current
        
        battery lifetimes !
  - 80% to 60% of traditional BT chips
  - designing a connectionless data model
- lowest possible latency
- widest possible range of interoperable devices and application

Acheiving low power

By keeping the radio off
- lower standby time
- faster connection
- lower peak power
BLE only use 3 advertising channels(vs. 16-32channlels)
- RF is on for 1.2ms vs 22.5ms
Idle current is dominated by deep sleep current
- sensor type send data less often (0.5 to 4s)
- RF current is neligible due to low duty cycles
- Protocols
Faster connections
- a device that is advertising is able to connect to a scanning device
- The devices can connect and sendand acknowledge data in 3 ms
- vs classic BT 100ms
Lower Peak Power
- BLE uses relaxed RF parameters
  - GFSK modulation index increased(From 0.35 to 0.55)
- Packet length restricted
  - Together with GFSK gives lowest complexity transmitter / recevier
  - This results in a lower peak power

Data rate and throughput

NOT ABOUT data rate/ throughput
- about 260kbps maximum data rate
- concentrates more on lowest possible poewr consumption
ABOUT transferring state
- small, infrequent bits of data
- owest possible poewr consumption
- lowest latency

PHY Layer

Split the 2.4Ghz ISM band into 40 channels
- 3 Advertising Channels
- 37 Data channels
- $f_n = 2402+2n$Mhz
GFSK Modulation
- Modulation index 0.5, better range than the classic
  - allows use of fewer advertising channels
  - reduces power consumption
  - increases connection speeds
- Can reuse existing RF parts in BTchip
  - minimal additional cost in dual-mode chips

Master/ slave topology

Master is typically the central device
Salve is typically the peripheral device
Slave is very VEry power sensitive
- power consumption
Master is time sensitive
- latency

Separate adveritisng dand data channels

Data channels
- used to transfer reliable data robustly
- adaptive frequency hopping over 37 channles
- fast acknowledgement scheme
- if data doesnt get through, resent on next freqeuncy
Advertising channels
- 402, 2426, 2480Mhz.
  - it would avoid interference with Wi-Fi traffic
- Used by peripherals to advertise presence
  - when first power on
  - why they have data to send - central devices connect and get data
  - just to broadcast data to anybody scanning

Security

uses AES-128 with CCM encryption engine
Use Key Distribution to share various keys
- Identity Resolving Key is used for privacy
- Signing Resolving Key provides fast authentication without encryption
- Long Term Key is used for encryption
Pairing encrypts the link using a Temporary Key
- derived from passkey, NFC pairing, public key exchange (v1.1);
- then distribute keys.
Asymmetric key model:
- slave gives keys to master with a diversifier
- slave can then recover keys from the diversifier

Encryption

RFC 3610 based AES-128 encryption:
- Counter Mode Cipher Block Chaining Message Authentication Code
  - Counter mode CBC-MAC = CCM.
Each new data packet has a Message Integrity Check:
- 39 bit counter, 1 direction bit;
- 64 bit Initialization Vector 32 bits contributed by each device;
- MIC is 32 bits in length
MIC is separate from the CRC
- CRC can allow immediate acknowledgment;
- packet is only sent to host after MIC checked
- lowest peak power

Survaviblity

Robustness to Vital for Bluetooth
- it must be robust against 2.4 GHz ISM band interference
- Wi-Fi, 802.15.4, X-10, proprietary, etc
Coexistence is Vital
- should not interfere with existing Wi-Fi infrastructure/ad-hoc network;
- Adaptive Frequency Hopping is needed
- FCC recognizes this as the best way to avoid interference;
- Discovering devices / connecting devices should not break Wi-Fi
- It must not affect Bluetooth headsets

Power Consumption

Relative consumption
- Sleep time is way more longer
- power mode 1 : 3us wake up time consuming 235uA;
- power mode 2: wake up via sleep timer consuming 0.9uA
- power mode 3: via external interrupt consuming 0.4uA
Power consumption during the connection event:
- between connection events: power mode 2
- turning off: voltage regulator, processor, oscillator
- active: sleep timer, RAM and registers retained
- going active: via I/O interrupt or expiring sleep timer

Chapter 10 - WPAN/WBANs.Zigebee

Fri, 10 May 2019 00:00:00 +0000

WPAN/WBANs.Zigebee.m

IEEE 802.15 WG

Specify WPAN standard
Wireless Personal Area Network
TG 1 802.15.1: WPAN/Bluetooth
- defines PHY and MAC of Bluetooth
- standard issued in 2002 and 2005
TG 2: 802.15.2: coexistence
- coexistence of WPANs with other networks in unlicensed band;
- EEE 802.15.2-2003 published in 2003 and then ”hibernated”.(休眠)
high rate WPAN
- 802.15.3-2003 is a MAC and PHY standard for high-rate (11 to 55 Mbit/s) WPANs;
- 802.15.3a: UWB PHY… no agreement when choosing PHY (MB-OFDM vs. DS-UWB);
- 802.15.3b-2005: improve implementation and interoperability of the MAC;
- 802.15.3b-2009: mm-wave-based PHY, 57-64Ghz unlicensed band, >2Gbps
TG 4: Low Rate WPANs
- long battery life, low data rate, low complexity;
- 802.15.4 standard released in May 2003;
- many networks runs on top of 802.15.4: ZigBee, 6LoWPAN, WirelessHART, etc.
Enhancements of 802.15.4
- 802.15.4a-2007: additional PHYs, e.g. UWB pulsed radio;
- 802.15.4-2006: clarification of the original standard;
- IEEE 802.15.4c: adaptation to unlicensed bands in China;
- IEEE 802.15.4d: adaptation to unlicensed bands in China;
- IEEE 802.15.4e: enhancements for industrial apps, e.g. channel hopping;
- IEEE 802.15.4f: active RFID systems;
- IEEE 802.15.4g: smart utility networks: large networks with a lot of end systems.
TG 5 Mesh networking
- two parts: low rate and high rate mesh networks;
  - low rate: IEEE 802.15.4-2006 MAC
  - high rate: IEEE 802.15.3/3b MAC;
- common features: network initialization, addressing, multihop unicasting;
- low rate: multicasting, broadcasting, portability, trace route and energy saving
TG 6 Body Area Network
- low-power short range standard, draft in 2011
TG 7: visible light communication
work in progress

ZigBee

developed by ZigBee Alliance
on top of IEEE 802.15.4
Particular implementation of those features specified in IEEE standard
Toptology in
- Centralized star
- Cluster-tree-based
- full mesh(requires additional routing protocol)
Specifics:
- low-rate (even compared to Bluetooth)
- extremely low power consumption
- example of applicability: sensor networks

Comparison with other technologies

IEE 802.11x technolgies

3x more expensive than Bluetooth
5x the power consumption of Bluetooth

Reason for Zigbee

low cost, high reliability, very long battery life
high security, self-healing properties, larger number of nodes supported
ease of deployment, guaranteed delivery, route optimization
NOT CHOOSING
- Very specific apps
- BLE Exists

ZigBee application

Wireless sensor networks

ZigBee Protocol Overview

IEEE 802.15.4 PHY

Three low power unlicensed radios:
- 2.4Ghz: 250Kbps(EU) 16 channels (ch11-ch26);
- 915Mhz: 40Kbps(US) 10 channels(ch1 - ch10)
- 868Mhz: 20Kbps(Europe and Japan) 1 channel (ch0)
Cahnnels and modulation in 2.4Ghz
- 16 channels , each 5Mhz wide ch 11-26
- actual throughput, 50% of 250Kbps due to overheads
  - overheads: addressing, security, error control
- DSSS (direct sequence spread spectrum ) channel access
- O-QPSK modulation
Other responsiblities of PHY
- detecting transmissions from new nodes
- assessing quality of links with other nodes

IEEE 802.15.4 MAC

Functionlity
- CSMA/CA
- max.length of packet is 127bytes (2 bytes for CRC)
- guarantees? transmissions
Two modes of operation
- Acknowledge
- Unacknowledge
How ACK mode is implemented
- setting ACK bit in a forward packet
- if set: receiver ACKs correct reception
- if no: ACK is received with some time, retransmission

Device types

FFD (Full Function Device)
- capable of all the features and always “on”
- routing/coordination/network formation
- can talk to other FFDs and RFDs
- FFDs require more power
RFD (Reduced Function Device)
- Sometimes called leaf nodes
- simple netoworking functions
- end systems in a sensor network
- can talk to FFD only

Logical entities

Full Function Device (FFD)	Reduced Function Device (RFD)
Found in any topology	Found only in start topology
Can be a network co-ordinator	Cannot be a network co-ordinator
Can talk to any type of device	Talks only to FFD
Usually main powered	Usaully battered powered

Network Coordinator
- FFD, one per work
- Create a network , assign channel/address
- adds new devices to a network
- constant power supply
- sometimes serves as a gateway
- a node may join if the coordinator is up
- if down, already existing node may continue to network
Router Functionality
- FFD devices serving as a relay node
- range extension
- constant poewr suplly
- sores packets sent to sleeping nodes
- can be used to access the network
End Device
- FFD/RFD
- low power consumption
- sleeping modes are defined
- communication through routers

Network Topologies

Star Topology

Advantage	Disadvantage
small delay due to single hop	single point of failure(co-coodinator)
	end devices cannot communicate directly

Cluster-tree Topology

two levels of hierarchy
more nodes can be added via routers
large coverage areas
several paths in-between end nodes

Mesh Topology

extension of cluster-tree topology
connections to deveices at different layer feasible
RFD are still unable communicate directly
DELAY CAN BE REDUCED but COMPLEXITY of ROUTING is HIGH

Access methods

non-beacon access
- transmit at anytime when channel is idle
- “free-for-all” environment
beacon-based access
- coordinator generates a superframe identified at beacon time
- all nodes are synchronized
- nodes transmit only i its designated time slot
- superframe may contain common slot when stations compete
- in-between: could go sleeping

Creating a network

Initialization for coordinator
- a node searches for coordinators on all channels;
- if no coordinators, starts its own one using unique 16-bits PAN ID;
Initialization for end nodes:
- scanning all available channels;
- can detect router and coordinator with the same PAN ID
- if yes, device with strongest SNR is chosen;
  - end devices sends “can i join”
  - address is allocated if there is place for a new node
Parameters set by a coordinator:
- max number of child devices allowed per router
- max number of hops from the co-ordinator to the most distant device

###

Network Example

Addressing

Three types of IDs
- MAC address (64-bits ID)
- network address(16-bits ID)
- name of device

Unicasting and broadcasting

Usage of address
- while joining: extended MAC address
- while connected: short network address
Unicast
- network address is used as destination address in MAC header
- message is routed in the network
- destination accepts the message, others drop
- destination answers with ACK
- the process is a bit more complex: local ACKs
Broadcasting is used when
- joining or rejoining network
- discovering routes in the network;
- should be minimized
Broadcasting
- MAC address is 0XFFFF
- all active devices receive and analyse the message.
- all active FFD devices retransmit it
ACKing broadcast message
- no explicit active ACKs
- passive ACKing: listening whether all neighbors retransmitted
  - if not repeat the transmission

Routing and route discovery

General consideration
- star topology no need routing
- cluster-tree and mesh topologies need routing
- more than one approach
Cluster-tree topology
- tree-routing
  - works fine for small networks
- route discovery
  - work when network is unstable or large
Mesh topology
route discovery is only possible with AODV
Tree routing
- use tree hierarchial structure
- first decision: whether to go up or down in hierarchy
- examining
  - if destination is a descendant, the device sends the packet to a child;
  - otherwise, send it to a parent
- upon reception by a node
  - accepts if the destination is a directly connected child
  - otherwise: sends to a parent
BAD: path could be longer than needed

GOOD: quite stable as tree structure is guaranteed

Sleeping modes

General facts

reduce power consumptions
still retain network address while sleeping
parent device buffers packets while child is asleep
upon wake up it checks whether there are some in store

Two types of sleeping mode

Cyclic sleep
additional modes : can be controled , pin sleep

Chapter 9 - NB-IoT as enabler for mMTC

Fri, 10 May 2019 00:00:00 +0000

NB-IoT as enabler for mMTC

NB-IoT

Narrow Band Internt of Thing （窄帶物聯網）
is a standards-based low power wide area (LPWA) technology developed to enable a wide range of new IoT devices and services。
significantly improves the power consumption of user devices, system capacity and spectrum efficiency, especially in deep coverage
10 years battery life
Each device habing TCP/IP stack

IoT market landscape

28 billions of connected devices by 2021
IoT market USD 19 trillions by 2026
More than 10⁴ companies involved by 2020

IoT Classification

Massive IoT
Mission-critial IoT

Massive IoT

Properties

Long range , link budget of 164dB
Power efficient, 10+year device battery life , 100x netowork energy efficiency
Massive Scale, 1+million devices/km^2
extreme simplicity , scaling lowest-end use cases

Massive IoT enablers

Comparison

NB-IoT implementation and band

Implementations

In-band LTE
Guard band LTE
standalone

Opeartioal frequencies

868 MHZ
LTE Bands

NB-IoT area

Marine cargo IoT

https://www.marinetraffic.com/

Container monitoring is IoT
Most cargo vessels are close coast
They use statellite links for IoT
use onshore NB-IoT infrastructure
- direct offloading
- ship-mounted relays
- UAV relays

Earth Curvature

Chapter 8 - Spatially-temporal traffic dynamics and URLLC service

Fri, 10 May 2019 00:00:00 +0000

Spatially-temporal traffic dynamics and URLLC service

General

Service Requirement

3GPP 5G Service

mMTC (massic Machine-Type Communication) 夠大
- Long Distance (link budge 164dB)
- Power efficiency (10+ years battery lifetime)
- Extremely dense (1+million devices/km²)
eMBB (enhanced Mobile Broadband) 夠寬
- Packet cell rate at 10Gbps
- Latency at air interface ~10ms
URLLC (Ultra Reliable Low Latency Communications) （夠低）
- Air interface latency <1ms
- Prbability of devliery 0.9999999

5G NR Services

New bandwidth-greedy services
- VR,AR
- High-rate video application (FHD+)
High-end IoT application
- Inter-robot communication
- V2V communcation, V stands for Vehicle
- inter-UAV communications
  - unmanned aerial vehicle (UAV)

Servicing Spatially-temporal traffic

Traffic Anaysis

Different time of day

Solution

Locailzation(off-loading ) using D2D(devices)
- A fraction of traffic can be localized
- Offloading onto direct links
On-demand service provisioning
- Mobile access points
- “Cell on whieels” (CoW), UAV
  - COW: portable mobile cellular site that provides temporary network and wireless coverage to locations where cellular coverage is minimal or compromised.

Traffic Localization (off-loading)

D2D Technologies

Wifi-direct, LTE-sidelink
3GPP plans to add NR-direct
Limitation
- Limited communication range
- Still limited support

D2D meshs

interference in adhoc network
relaying a mesh

Blockchain

Mobile AP

3GPP Supoort

UAV support in 3GPP
NR relaying/sidelink
Backhauling

Performance

Backhaul is critial
Dynamic optimization is critical
Interplay between no. of UEs and no. of UAVs

URLLC Service

High-end IoT application

Driven by new use-cases
Driven by elecronic evolution

Industrial Automation

Autonomous production lines
Traffic characteristics
- Low latency (few ms)
- High reliability (10^-5 BLER) (Block Error Rate)

Autonmous Driving

Future of car industry
Traffic characteristics
- Huge throughput
- Low latency

Healthcare : Remote surgeries

Traffic characteristics
- Extremely Low latency (<1ms)
- Extremely High reliability (10^-9)

Remote Diagnosis

NR+LTE

Addressing Latency

Main chanllenge
- NR frame duration : 1ms
- Latency <1ms
- How to conform?
Two principle ways
- Reservation/priorities
- Non-Orthogonal multiple access (NOMA)
  - International overlapping of data
  - Enable by flexible NR slot numberology

Addressing Reliability

Bloackage may or may not lead to outage(中斷)
- Case 1: blockage leads to lower MSC scheme
  - MSC: Mobile Switching Service Centre
- Case 2: bloackage leads to outage
Solution
- Case 1: provide more resources
  - Bandwidth reservation
  - Isolated deployments
- Case 2: find a new path
  - 3GPP multi-connectivity
  - Dense deployments
Multi-connectivity
- avoiding outage!
Bandwidth reservation
- Alleviating lower MCSs(Modulation and Coding Scheme)

Chapter 7 - Massive machine-type communications technologies (MTC)

Fri, 10 May 2019 00:00:00 +0000

Massive machine-type communications technologies (MTC)

IoT

Internet of Thing

Consumer vs Industrial IoT domains

Industrial IoT is similar to the consumer IoT,
but the difference is that it has this is used in a commercial area that is industries.

Contemporary IoT connectivity Solution

They connect with each other using different standards for different applications

Short-Range Access Technologies for IoT

Historical solutions (Bluetooth, IEEE 802.15.4, IETF stacks,…) are evolving to maintain competitiveness in growing IoT market
IEEE 802.11ah(HaLow), low-cost, large-scale connectibity across massive deployments
Unlicensed Low-Power Wide Area (LPWA) networks rapidly emerge to support early stages of the IoT development, until standardized cellular M2M solutions enter the market.

Next-Generation Wireless IoT Technology

Fifth-generation (5G) wireless technology is targeting to offer support for numerous IoT applications

5G Performance Targets Are Set Clearly

IMT-2020

Tactile Internet

The Tactile Internet will be the next evolution of the Internet of Things (IoT), encompassing human-to-machine and machine-to-machine interaction.
It will enable real-time interactive systems with a raft of industrial, societal and business use cases.

Chapter 6 - 5G Cellular and New Radio

Fri, 10 May 2019 00:00:00 +0000

5G Cellular and New Radio

Satisying growing traffic demands

Is 4G enough

1000Mbps for all subscribers in a cell
- Cell radius ~500m to 2Km
- Density of users : city centre -0.1 to 0.1 humans/m²
The traffic growth is so huge
Performance metrics
- Shannon Channel capacity
  - $C=Blog_2(1+S)$
  - B is the bandwidth
  - S is the SINR(signal-to-interference plus noise ratio)
    - $S=\frac{P_R}{BN+I} $
    - $P_R$ is the signal power at the receiver
    - $N$ is the thermal noise, constant
    - I is the aggregated interference
- Signal power at the receiver
  - $P_r = P_TAd^{-Y}$
  - $P_T$ is the emitter power at the transmier
  - A is the constant that depends on antennas/frequency
  - Y is the “path loss exponent” deponds on environment
FINAL VERISON = $C=Blog_2{(1+\frac{P_R}{BN+I})}$
- PHY Layer mechanisms
  - FEC,MIMO,ARQ, 90% to shannon
- Increse emitted power
  - may increase interference
- Decrease thermal noise
  - Constant up to 0.6Thz
  - may use superconductor
- Decrease interference
  - Logarithmic increase of C
- Increase bandwidth
  - Almost linear increase of C
- Network Mechanisms
  - Better Spatial frequency reuse

Increasing bandwidth

buy more licenced frequencies
- Commercial netwoks(cellular networks)
- Exclusive access
- Ablity to use higher transmission power >1mW
- High costs and risks
- Less than 100-500Mhz overall in a country(less than 3Ghz )
Use the unlicensed spectrum
- ISM bands (Industrial, scientific, medical bands)
- Extreme interference from Wi-Fi-s
Spectral Efficiency
- the information rate that can be transmitted over a given bandwidth in a specific communication system
Quadrature Amplitude Modulation
- PSK+ASK :S(t)= $Acos(wt+\phi)$, modulating $w $and $\phi$
Higher frequency then more bandwidth available
5G: millimeter wave (mmWave)
- 28Ghz
- 60Ghz(802.11ad)
- 72Ghz
- Postives
  - Highly directional antennas
- Negative
- Blockage by humans
- Large propagation losses
- Realistically up to 100m
B5G,6G: teraherz(sub-mmWave)
- 275-325 GHz: 50Ghz of bandwidth
- IEEE 802.15 3d”100Gbps wireless”
- Positive
  - Even more directivity
  - Hugh channel capacity
- Negative
  - Atmospheric absorption（大氣吸收）
  - Blockage by Human
  - Extreme propagation losses
- up to 10-20m realstically
  5G and New Radio Interface

5G/5G+ systems as enablers

Resembles properties of CPS
- CPS is Technological systems where physical and cyber components are tightly integrated(smartphone)
Moves us closer to tactile Internet（觸覺互聯網） conecpt， next IoT
Has to be supoorted by 5G/5G+ mobile cellular systems
At least two of the following are required
- High throughput
- High reliability
- Low latency
Reliable service over inherently unreliable medium

Envisioned 3GPP 5G services

Enhanced mobile broadband(eMBB)
- data-driven use cases requiring high data rates across a wide coverage area.
Massive machine-type communications(mMTC)
- NB-IoT technology
Ultra-reliable low-latency services (URLLC)
- Not yet available and no dates annouced

5G evolution or revolution

5G/5G+ systems are heterogeneous(同質) in nature
- New Radio(NR) RAT(28,38,72GHz)
  - RAT (Radio Access Technology)
- Multi Rat support,,BT,WIFI,3G,4G,LTE
- Advanced features: D2D, relays, femto/micro BSs.
  - D2D : Device to Device
- SDN/NFV capabilities for control plane
  - SDN: Software Defined Networking
  - NVF: Network Virtualization Function
NR is expected to support URLLC service
delivery up to 10Gps per AP
upper bound latency
provide reliability

Propagation in mmWave band

Highly complex compared to microwaves
- Multiple paths
- Material dependent
- Spatial correlation
  - the channels between different antennas are often correlated and therefore the potential multi antenna gains may not always be obtainable
- Temporal correlation

Path blockage phenomenon

Very small wavelengths
- 30Ghz ~1mm
  - Cannot penetrate through objects
  - Cannot travel around
Blockage happens at sub-second scales
- Models for various environments needed

Beam tracking（波束追蹤）

Massive MIMO to form directional radiation patterns
- Linear arrays HPBW～102/N
Positive effects
- Much less interference
- Noise-limited regime?
Negative effects
- Beam alignment needed
- Array swtiching time ~2us
- Exhaustive vs hierarchical
- Delay and loss in capacity ？

Extreme and complex path loss

Addressing Latency

Main chanllenge
- NR frame duration : 1ms
- Latency <1ms
- How to conform?
Two principle ways
- Reservation/priorities
- Non-Orthogonal multiple access (NOMA)
  - International overlapping of data
  - Enable by flexible NR slot numberology

Addressing Reliability

Bloackage may or may not lead to outage(中斷)
- Case 1: blockage leads to lower MSC scheme - MSC: Mobile Switching Service Centre
  - Case 2: bloackage leads to outage
Solution
- Case 1: provide more resources
  - Bandwidth reservation
  - Isolated deployments
- Case 2: find a new path
  - 3GPP multi-connectivity
  - Dense deployments