1. Cordless Systems and Wireless Local Loop
张宝贤：《无线网络技术》
Cordless Systems and Wireless Local Loop
Chapter 11

2. Cordless System Operating Environments
Residential – a single base station can provide in-house voice and data support
Office
A single base station can support a small office
Multiple base stations in a cellular configuration can support a larger office
Telepoint – a base station set up in a public place, such as an airport

3. Design Considerations for Cordless Standards
Modest range of handset from base station, so low-power designs are used
Inexpensive handset and base station, dictating simple technical approaches
Frequency flexibility is limited, so the system needs to be able to seek a low-interference channel whenever used

4. Time Division Duplex (TDD)
TDD also known as time-compression multiplexing (TCM)
Data transmitted in one direction at a time, with transmission between the two directions
Simple TDD
TDMA TDD

5. Simple TDD
Bit stream is divided into equal segments, compressed in time to a higher transmission rate, and transmitted in bursts
Effective bits transmitted per second:
R = B/2(Tp+Tb+Tg)
R = effective data rate
B = size of block in bits
Tp = propagation delay
Tb = burst transmission time
Tg = guard time

6. 每传输一个burst占用信道时间:Tp+Tb+Tg

7. Simple TDD Actual data rate, A: Combined with previous equation:
A = B /Tb
Combined with previous equation:
The actual data rate is more than double the effective data rate seen by the two sides

8. TDMA TDD Wireless TDD typically used with TDMA # 1 # 2 # 3 用户端 基站
A number of users receive forward channel signals in turn and then transmit reverse channel signals in turn, all on same carrier frequency
# 1
# 2
# 3
用户端 基站
frame ……
UL：up link
DL: down link
基本上消除了Simple TDD方案中,每次burst传输所占用的
传播时延Tp. UL DL
TDMA TDD
简化示意图

9. TDMA TDD Advantages of TDMA/TDD:
Improved ability to cope with fast fading
通过接收器配备两个间隔一个波长的天线——这样做的好处在于:当其中一根天线遇到明显的快衰落(fast fading)时，另一根很可能不会。
虽然移动终端不太可能象基站那样安装两个天线，但基站可以选择信号强的那个天线进行信号发送——从而大大降低移动终端可能遭遇的衰落——因为前向和后向使用的频率相同
大大提高了带宽利用率（与simple TDD相比）
通过动态时隙分配——时隙变长、动态预约、帧长可变
Tightly packed transmissions in each directions

10. DECT Protocol Architecture

11. DECT Protocol Architecture
Physical layer – data transmitted in TDMA-TDD frames over one of 10 RF carriers
Medium access control (MAC) layer – selects/ establishes/releases connections on physical channels; supports three services:
Broadcast
Connection oriented
Connectionless
Data link control layer – provides for the reliable transmission of messages using traditional data link control procedures

12. Differential Quantization
Speech signals tend not to change much between two samples
Transmitted PCM values contain considerable redundancy
Transmit difference value between adjacent samples rather than actual value
If difference value between two samples exceeds transmitted bits, receiver output will drift from the true value
Encoder could locally replicate receiver output and additionally transmit that difference

13. Differential PCM (DPCM)
Since voice signals change relatively slowly, value of kth sample can be estimated by preceding samples
Transmit difference between sample and estimated sample
Difference value should be less than difference between successive samples
At the receiver, incoming difference value is added to the estimate of the current sample
Same estimation function is used

14. Adaptive Differential PCM (ADPCM)
Improve DPCM performance using adaptive prediction and quantization
Predictor and difference quantizer adapt to the changing characteristics of the speech
Modules
Adaptive quantizer
Inverse （反向） adaptive quantizer
Adaptive predictor

15. ADPCM Encoder

16. ADPCM Decoder

17. Subject Measurement of Coder Performance （编码器性能的主观测量）
Subjective measurements of quality are more relevant than objective measures
Mean opinion score (MOS) – group of subjects listen to a sample of coded speech; classify output on a 5-point scale
MOS scale is used in a number of specifications as a standard for quality

18. Wireless Local Loop
Wired technologies responding to need for reliable, high-speed access by residential, business, and government subscribers
ISDN, xDSL, cable modems…last mile techniques
Increasing interest shown in competing wireless technologies for subscriber access
Wireless local loop (WLL), also called fixed wireless access， Wireless MAN

19. WLL 与移动电话服务的几个区别 WLL：源于1969年，但到1998年开始运作(serious operation)
通常要求高速数据通信支持能力
可以采用定向天线
用户是不移动的（如房子），所以没有了handover的问题
WLL：源于1969年，但到1998年开始运作(serious operation)

20. WLL Configuration

21. Advantages of WLL over Wired Approach
Cost – wireless systems are less expensive due to cost of cable installation that’s avoided
Installation time – WLL systems can be installed in a small fraction of the time required for a new wired system
Selective installation – radio units installed for subscribers who want service at a given time
With a wired system, cable is laid out in anticipation of serving every subscriber in a given area
当然，WLL也有劣势，如安装之后受环境因素影响大，如楼群建设而导致的障碍物（未完待续）

22. Propagation Considerations for WLL
Most high-speed WLL schemes use millimeter wave frequencies (10 GHz to about 300 GHz)
There are wide unused frequency bands available above 25 GHz
At these high frequencies, wide channel bandwidths can be used, providing high data rates
Small size transceivers and adaptive antenna arrays can be used

23. Propagation Considerations for WLL
Millimeter wave systems have some undesirable propagation characteristics
Free space loss increases with the square of the frequency; losses are much higher in millimeter wave range
Above 10 GHz, attenuation effects due to rainfall and atmospheric or gaseous absorption are large
Multipath losses can be quite high
受上述因素限制，通常，WLL的服务半径在几公里范围

24. Fresnel Zone 菲捏耳区
How much space around direct path between transmitter and receiver should be clear of obstacles? （发射器和接收器间的直线上多大的空间内的障碍物应该被清除？）
Objects within a series of concentric circles around the line of sight between transceivers have constructive/destructive effects on communication
For point along the direct path, radius of first Fresnel zone:
S = distance from transmitter
D = distance from receiver

25. Fresnel Zone 菲捏耳区 沿着或接近LOS直线的地方必须避免障碍物，包括树叶
发现：若两收发器间任意点的第一菲捏耳区半径的0.6倍无
障碍的话，由障碍而产生的衰减可以忽略
如：两个收发器相距10km，载频2.4GHz,则两收发器中间
点的第一菲捏耳区半径为17.7米，如果信号频率为
28GHz, 则同一点上R=5.17米

26. Atmospheric Absorption
Radio waves at frequencies above 10 GHz are subject to molecular absorption （分子吸收）
Peak of water vapor absorption at 22 GHz
Peak of oxygen absorption near 60 GHz
Favorable windows for communication:
From 28 GHz to 42 GHz
From 75 GHz to 95 GHz

28. Effect of Rain Attenuation due to rain
Presence of raindrops can severely degrade the reliability and performance of communication links
The effect of rain depends on drop shape, drop size, rain rate, and frequency
Estimated attenuation due to rain:
A = attenuation (dB/km)
R = rain rate (mm/hr)
a and b depend on drop sizes and frequency

29. Effects of Vegetation 植物效应
Trees near subscriber sites can lead to multipath fading
Multipath effects from the tree canopy are diffraction and scattering （衍射和散射）
Measurements in orchards (果园) found considerable attenuation values when the foliage (树) is within 60% of the first Fresnel zone
但树的出现并没有阻止通信，但需要有充分的应对措施，如前向纠错。
Multipath effects highly variable due to wind

30. OFDM (正交频分复用) 也称多路载波调制
OFDM在不同频率上使用多个载波信号，在每个信道上发送一些位，这与FDM类似。然而，在OFDM中，所有子信道为一个信息源所使用。
OFDM中所有副载波都是某一基频的整数倍，即：fb, 2fb, 3fb,…

31. OFDM (正交频分复用)
图中可以看出某个副载波的功率谱密度的峰值发生在其它副载波为0的点上——因而这些副载波具有最小的相互干扰。因此称这些副载波是正交的。

32. OFDM (正交频分复用) 优点： 频率选择性衰落(frequency-dependent fading)只影响一些子信道而不是整个信号。
恰当的FEC可以很有效地保护这样的信号
在多径环境下，可以消除码间干扰(intersymbol interference, ISI). 随着比特（或信号）之间距离变小，ISI对更高速率的数据流有更大的影响。
OFDM系统中，每个子信道上数据速率变为原始数据率的1/N, 则每个信号(symbol)占的时间变为原来的N倍，这样可以大大降低ISI效应。

33. Multipoint Distribution Service (MDS)
Multichannel multipoint distribution service (MMDS)
Also referred to as wireless cable
Used mainly by residential subscribers and small businesses
About 50 km range
Local multipoint distribution service (LMDS)
Appeals to larger companies with greater bandwidth demands
2-5 km

34. Advantages of MMDS
MMDS signals have larger wavelengths and can travel farther without losing significant power
Equipment at lower frequencies is less expensive
MMDS signals don't get blocked as easily by objects and are less susceptible to rain absorption

35. Advantages of LMDS Relatively high data rates
Capable of providing video, telephony, and data
Relatively low cost in comparison with cable alternatives
但受LOS和雨的影响

36. 802.16 Standards Development （LMDS的一个标准）
Use wireless links with microwave or millimeter wave radios
Use licensed spectrum
Are metropolitan in scale
Provide public network service to fee-paying customers
Use point-to-multipoint architecture with stationary rooftop or tower-mounted antennas
Now starts to support mobile users and related standardization is still in progress

37. 802.16 Standards Development
Provide efficient transport of heterogeneous traffic supporting quality of service (QoS)
Use wireless links with microwave or millimeter wave radios
Are capable of broadband transmissions (>2 Mbps)

38. Standard History
2006
802.16a Fixed Broadband Wireless Standard for 2-11 GHz Non-LOS Systems (Inactive)
65 members
1999
2002
2003
2004
2005
802.16c System Profiles for GHz LOS Systems (Inactive)
343 members
Membership
Time
IEEE Working Group Started
55 members
802.16e Combined Fixed and Mobile Amendment for <11 GHz Licensed Systems (Formally approved in December 2005)
Fixed Broadband Wireless Standard for GHz LOS Systems (Inactive)
WiMAX Forum now certifying IEEE fixed products!
IEEE e mobile products will follow!
802.16f Fixed MIBs
/Cor1 Corrigendum
Fixed Broadband Wireless Standard
(Revised : Covers <11 GHz NLOS & GHz LOS Systems)
This page represents the history of standard. IEEE working group started from Its progress is quite slow before year a is published at that time. It uses single carrier modulation and only work in LOS environment. In the middle of 2003, Intel begin to actively involve into And the progress is much more accelerated. In 2004, d is published. It revolutionary introduced OFDM technology to conquer nLOS fading. In the Dec. of 2005, e is approved, which supports mobile broadband access with OFDMA technology.

39. Standard Evolution
Fixed Applications
(licensed/unlicensed)
Cor1
Corrections
802.16e
Combined Fixed and Mobile Applications
(licensed)
802.16f
Fixed MIBs
802.16g
Fixed and Mobile Management (expected to complete in March 2007)
Planned j
Multi-hop/Relay Project
(expected in 2008)
Planned i
Mobile MIBs Project
(expected in March 2007)
802.16h License Exempt
Co-existence Procedures
License-exempt TV bands,
Non-exclusive licensed bands
(US: FCC MHz)
Standard
Under development
Future project
This page represent the standard evolution path d support fixed application in licensed/unlicensed frequency band. And e support both fixed ad mobile application at licensed band f ad i define MIBs for fixed and mobile application.
The g is still on progress which will define the management procedure. And h is going to define the Base Station co-existence at license exempt band.
Mobile Multi-hop/Relay (MMR) Study Group is planning x to introduce multi-hop or mesh technology to improve the WiMAX coverage. It is still in PAR creation phase.
MIB: Management Information Base
standard evolution based on latest technologies

40. Salient Features Scalability High Data Rates QoS Mobility Security
Scalable PHY for flexible channel bandwidths ( MHz)
as global RF band allocations vary (e.g.: 2.3, 2.5, 3.5 GHz)
Flexible frequency re-use schemes for network planning
QoS
QoS with Service Flows, Advanced Scheduling
Framework, Adaptive Modulation & Coding, ARQ, H-ARQ
Security
EAP authentication, Encryption with AES-CCM,
CMAC Authentication, X.509 Certificates, Key Binding,
Mutual Authentication, Device and User Authentication
Mobility
Secure Handover, Optimized Hard Handover, Multicast, Broadcast, Paging, Power Management with Sleep and Idle Modes
High Data
Rates
Larger MAC frames with low overhead,
Adaptive Modulation, Advanced FEC, H-ARQ,
Beamforming (AAS), Space-Time Transmit Diversity, MIMO
Advanced Encryption Standard (AES) in Counter with CBC-MAC (CCM) AES-CCM = Advanced Encryption Standard (AES) in Counter with CBC-MAC (CCM) Mode
CMAC = Cipher-Based Message Authentication Code
EAP = Extensible Authentication Protocol

41. 802.16传输环境

42. WiMAX Forum WiMAX: Worldwide interoperatability for Microwave Access
The WiMAX Forum, founded in April 2001, brings together leaders in the communications and computing industries to drive a common platform for the global deployment of IP-based broadband wireless services.
The WiMAX Forum certifies products for conformance and interoperability based upon the IEEE and ETSI Hyperman standard.
WiMAX: Worldwide interoperatability
for Microwave Access
ETSI: European Telecommunications Standards Institute

43. WiMAX Forum Technical Liaisons
IETF
16ng (i.e., IP over IEEE (e) Networks WG) – Will publish RFCs for IPv6 and Ethernet CS (Convergence Sublayer) operation based on NWG (Network Working Group) specification
Other dependencies – AAA, RADEXT, MIPv4/v6
Evaluating NETLMM
IEEE
Close coordination with TGs
3GPP
Liaison with TSG-SA for mobile WiMAX Interworking
23.882,
3GPP2
Liaison proposal under discussion
RADEXT: RADIUS Extensions Working group
AAA: Authentication, Authorization and Accounting
MIPv4/v6: MOBILE IP v4/v6 working group
Network-based Localized Mobility Management BOF (netlmm)
TSG-SA: TSG Service and System Aspects
TSG: 无线接入网络

44. Industry Mobile WiMAX Solutions Roadmap
2006
2007
2007
2008
2008
2009
PoC=Proof of Concept
* Names and Brands may be claimed as property of others

45. Mobile WiMAX = Mobile Internet

46. Pre-commercial Services Overview
Media service
T-DMB service
M-log service
VOD/MOD service
Entertainment service
Communication service
PTA (Push-to-all) service
Multi-party video conferencing service
Community service
Data service
Internet access service
Search service
Specialized service
PIS (Personal Intelligent Service)
Mydesk service
@mint service
T-DMB：Terrestrial Digital Multimedia Broadcasting
M-Log can graph data from a wide range of data loggers from different manufacturers
KT WiBro provides broadband wireless internet access service comparable with wired internet access service for anywhere anytime even when you are moving.
KT WiBro search service provides integrated search services (dictionary, knowledge, image, and others) and finance/stock, tourism, and differentiated map search service based on LBS (Location Based Service).
PIS (Personal Intelligent Service) is personally fitted package. Using Push technology, PIS delivers “personally fitted contents package service” in real time based on each person’s interest and taste such as culture, sports, childcare, and others.
Mydesk service is a ubiquitous personal search engine. Through KT WiBro portable/handheld device, people can access personal web-storage as well as personal PC.
@mint service is next generation platform implemented for WiBro based on real-time multimedia technology, and provides real-time bidirectional group study service and bidirectional live quiz service.

47. IEEE 802.16 Protocol Architecture
-Tanenbaum, computer networks, 第四版

48. Protocol Architecture
Physical and transmission layer functions:
Encoding/decoding of signals
Preamble generation/removal
Bit transmission/reception
Medium access control layer functions:
On transmission, assemble data into a frame with address and error detection fields
On reception, disassemble frame, and perform address recognition and error detection
Govern access to the wireless transmission medium

49. Protocol Architecture
Convergence layer functions:
Encapsulate PDU framing of upper layers into native MAC/PHY frames
Map upper layer’s addresses into addresses
Translate upper layer QoS parameters into native MAC format
Adapt time dependencies of upper layer traffic into equivalent MAC service

50. IEEE 802.16.1 Services Digital audio/video multicast Digital telephony
ATM
Internet protocol
Bridged LAN
Back-haul
Frame relay

51. MAC Management Messages
Uplink and downlink channel descriptor
Uplink and downlink access definition
Ranging request and response
Registration request, response and acknowledge
Privacy key management request and response
Dynamic service addition request, response and acknowledge

52. MAC Management Messages
Dynamic service change request, response, and acknowledge
Dynamic service deletion request and response
Multicast polling assignment request and response
Downlink data grant type request
ARQ acknowledgment

53. Physical Layer – Upstream Transmission
Uses a DAMA-TDMA technique
Error correction uses Reed-Solomon code
Modulation scheme based on QPSK, QAM-16, or QAM-64

54. Physical Layer – Downstream Transmission
Continuous downstream mode
For continuous transmission stream (audio, video)
Simple TDM scheme is used for channel access
Duplexing technique is frequency division duplex (FDD)
Burst downstream mode
Targets burst transmission stream (IP-based traffic)
DAMA-TDMA scheme is used for channel access
Duplexing techniques are FDD with adaptive modulation, frequency shift division duplexing (FSDD), time division duplexing (TDD)
FDD: 上下行信道是对称的 ——不利于非对称业务