OFDMA Orthogonal Frequency Division Multiple Access

Transcription

1 ECE 645 Wireless Communication Systems Presentation OFDMA Orthogonal Frequency Division Multiple Access Presented by: Chenxi Bao Chao Xie Nan Wu

2 Outline Theory of OFDM Architecture of RAN and CN Compare OFDMA with CDMA

3 Theory of OFDM 1. Introduction OFDM is a multi carrier digital modulation technique in which a high bit rate serial data stream is separated into a large number N of narrowband and low data rate sub channels each of which modulates a single sub carrier, and each sub carrier transmits symbols in parallel. Channel bandwidth is divided into multiple sub channels orthogonal to each other. Sub carriers should be modulated by using BPSK, QPSK, 16 QAM, or even 64 QAM modulation depending on how severe the channel condition is. The better channel condition is, the higher constellation points request. Chenxi Bao

4 Theory of OFDM 1. Introduction Due to the duration of each symbol is longer enough than the spread delay, OFDM is effective in avoiding inter symbol interference (ISI) caused by multi path propagation delay in a frequency selective fading environment, therefore OFDM is low sensitivity to time synchronization errors. Theoretically, with N is large enough, the bandwidth of each sub channel can be divided only 1Hz. Due to orthogonality, the energy at the central frequency becomes exactly zero such that the cross talk between subchannels (ICI) can be eliminated even spectra overlapped in frequency domain. Chenxi Bao

5 2. Mathematic description (1) Orthogonality (2) FFT algorithm First assume: Theory of OFDM T 1 k xj () t = e dt = T 0 { j2 π ( fj f ) 1, j= k 0, j k Δ f = 1 f N j f T = = k s T, f k = k = T k NTs Samples: ynt ( ) s N 1 1 = Ye k N k = 0 2π j kn N Periodicity: N 1 2π 1 2 ( ) N π j k+ N n j kn N N j2π n k+ N= k = k = k n= 0 n= 0 Y Ye Ye e Y Chenxi Bao

6 Theory of OFDM 3. Ideal OFDM digital communication system Chenxi Bao

7 OFDMA Chenxi Bao

8 OFDMA Frequency reuse in OFDM based system Self provisioning cells Intra cell interference free Inter cell interference avoidance Overlapping cell redundancy More flexibility Sub channelization can be performed according to individual channel condition Allow peak capacity access by one user if other uses are idle Configurable to circuit switched FDMA Suitable for burst packet network Chenxi Bao

9 Advantages of OFDM Can easily adapt to severe channel conditions without complex equalization Robust against narrow band co channel interference Robust against Inter symbol interference (ISI) and fading caused by multi path propagation High spectral efficiency Efficient implementation using FFT Low sensitivity to time synchronization errors Tuned sub channel receiver filters are not required (unlike conventional FDM) Facilitates Single Frequency Networks, i.e. transmitter macro diversity. Chenxi Bao

10 Disadvantages of OFDM Sensitive to Doppler shift Sensitive to frequency synchronization problems Inefficient transmitter power consumption, due to linear power amplifier requirement Chenxi Bao

11 Applications of OFDM ADSL and VDSL broadband access via POTS copper wiring. Certain Wi Fi (IEEE a/g) Wireless LANs. HIPERLAN/2 MMAC (multimedia access controller) DAB systems EUREKA 147, Digital Radio Mondiale, HD Radio, T DMB and ISDB TSB. DVB terrestrial digital TV systems DVB T, DVB H, T DMB and ISDB T. IEEE or WiMAX Wireless MANs. IEEE or Mobile Broadband Wireless Access (MBWA) systems. Flash OFDM cellular systems. Certain Ultra wideband (UWB) systems. Power line communication (PLC). MoCA home networking. Chenxi Bao

12 OFDM in future 4G communication system Some features of 4G system: Frequency band: 2 8GHz Bandwidth: 5 20MHz Data rate: 20Mbps or more Mobile top speed: 200kmph Combination of Multiple Input Multiple Output (MIMO) wireless technology with Orthogonal Frequency Division Multiplexing (OFDM) One of the most promising techniques to support high data rate and high performance in next generation communication systems. Chenxi Bao

13 Introduction of RAN (Radio Access Network) A radio access network (RAN) is part of a mobile Telecommunication system. It implements a radio access technology. It sits between the Mobile phone, and the core network (CN). The mobile phone is varyingly known as user equipment (UE), terminal equipment, mobile station (MS), etc., depending on the standard. Examples of radio access network: GRAN GSM radio access network GERAN GSM EDGE packet radio services UTRAN UMTS radio access network E UTRA LTE radio access network Chao Xie

14 System architecture for E UTRAN only network Chao Xie

15 E UTRAN Node B (enodeb) PART 1 The only node in the E UTRAN is the E UTRAN Node B (enodeb). Simply put, the enodeb is a radio base station that is in control of all radio related functions in the fixed part of the system. Function of enodeb 1. enodeb acts as a layer 2 bridge between UE and the EPC, by being the termination point of all the radio protocols towards the UE, and relaying data between the radio connection and the corresponding IP based connectivity towards the EPC. In this role, the enodeb performs ciphering /deciphering of the UP data, and also IP header compression and decompression. Chao Xie

16 E UTRAN Node B (enodeb) PART 2 2. The enodeb is also responsible for many Control Plane (CP) functions. i.e. controlling the usage of the radio interface, which includes, for example, allocating resources based on requests, prioritizing and scheduling traffic according to required Quality of Service (QoS), and constant monitoring of the resource usage situation. 3. The enodeb controls and analyses radio signal level measurements carried out by the UE, makes similar measurements itself, and based on those makes decisions to handover UEs between cells. Chao Xie

17 E UTRAN Node B (enodeb) PART 3 The figure below shows the connections that enodeb has to the surrounding logical nodes, and summarizes the main functions in these interfaces. Chao Xie

18 Evolved Packet Core Network (EPC) EPC : Core Network of LTE EPC is composed of MME, S GW, P GW, PCRF and HSS. Chao Xie

19 Mobility Management Entity (MME) PART1 Mobility Management Entity (MME) is the main control element in the EPC. Typically the MME would be a server in a secure location in the operator s premises. It operates only in the CP, and is not involved in the path of UP data. Authentication and Security When a UE registers to the network for the first time, the MME initiates the authentication, MME may repeat authentication when needed or periodically. The MME will calculate UEs ciphering and integrity protection keys and it controls the related settings in E UTRAN for UP and CP separately. To protect the UE privacy, MME also allocates each UE a temporary identity called the Globally Unique Temporary Identity ( G U T I ). Chao Xie

20 Mobility Management Entity (MME) PART2 Mobility Management The MME keeps track of the location of all UEs in its service area. When a UE makes its first registration to the network. The MME also participates in control signalling for handover of an active mode UE between enodebs, S GWs or MMEs. Managing Subscription Profile and Service Connectivity At the time of a UE registering to the network, the MME will be responsible for retrieving its subscription profile from the home network. Chao Xie

21 Serving Gateway (S GW) PART1 the high level function of S GW is UP tunnel management and switching. The S GW is part of the network infrastructure maintained centrally in operation premises. The S GW has a very minor role in control functions. It is only responsible for its own resources, and it allocates them based on requests from MME, P GW or PCRF. Chao Xie

22 Serving Gateway (S GW) PART2 During mobility between enodebs, the S GW acts as the local mobility anchor. The MME commands the S GW to switch the tunnel from one enodeb to another. The MME may also request the S GW to provide tunnelling resources for data forwarding. For all data flows belonging to a UE in connected mode, the S GW relays the data between enodeb and P GW. However, when a UE is in idle mode, the resources in enodeb are released, and the data path terminates in the S GW. Chao Xie

23 Packet Data Network Gateway (P GW) PART1 P GW is the edge router between the EPC and external packet data networks. It performs traffic gating and filtering functions as required by the service in question. Typically the P GW allocates the IP address to the UE, and the UE uses that to communicate with other IP hosts in external networks, e.g. the internet. It is also possible that the external PDN to which the UE is connected allocates the address that is to be used by the UE, and the P GW tunnels all traffic to that network. Chao Xie

24 Packet Data Network Gateway (P GW) PART2 P GW is the highest level mobility anchor in the system. When a UE moves from one S GW to another, the bearers have to be switched in the P GW. Chao Xie

25 Policy and Charging Resource Function (PCRF) PCRF is the network element that is responsible for Policy and Charging Control. It makes decisions on how to handle the services in terms of QoS, and provides information to the PCEF located in the P GW. Each PCRF may be associated with one or more AF, P GW and S GW. There is only one PCRF associated with each PDN connection that a single UE has. Chao Xie

26 Home Subscription Server (HSS) Home Subscription Server (HSS) is the subscription data repository for all permanent user data. It also records the location of the user in the level of visited network control node, such as MME. It is a database server maintained centrally in the home operator s premises. Chao Xie

27 System Architecture with E UTRAN and Legacy 3GPP Access Networks Chao Xie

28 Comparison of OFDMA & CDMA Review the principle of CDMA Code division multiple access (CDMA) is a multiple access technique where different users share the same physical medium, that is, the same frequency band, at the same time. Spread Spectrum technique Walsh Code Nan Wu

29 Orthogonality OFDMA It use orthogonal frequency to accomplish the orthogonality of traffic channels. CDMA It use orthogonal code to accomplish the orthogonality of traffic channels. Nan Wu

30 Traffic channel In OFDM system, we can use multi subcarrier and multitime slot to transmit data. In CDMA system, different users can use the whole traffic channel (1.25Mhz) to transmit data by using orthogonal codes. Nan Wu

31 Modulation In OFDMA system, Subcarriers should be modulated by using BPSK, QPSK, 16 QAM, or even 64 QAM modulation depending on how severe the channel condition is. In CDMA system, BPSK and QPSK are used as the basic modulation schemes in most practical communication systems. Nevertheless, higher order modulation techniques like 8 PSK and 16 QAM also are applied as additional transmission options to offer a high speed packet transfer at good propagation conditions. Nan Wu

32 Synchronization OFDMA Low sensitivity to time synchronization errors Sensitive to frequency synchronization problems CDMA CDMA system, which has been deployed, is a asynchronous system. Nan Wu

33 Interference OFDMA Intra symbol interference: effects which cause subcarriers within an OFDM symbol to lose orthogonality CDMA All other users signal can be seen as interference. Inter symbol interference: effects which cause interference between OFDM symbols Nan Wu

34 Architecture of EVDO REV.A Nan Wu

35 Network Elements MS Mobile Station BTS Base Transceiver Station BSC Base Station Controller MSC Mobile Switching Center HLR/VLR Home Location Register / Visiting location register. SS7 Signaling System 7 PSTN Public Switched Telephone Network RNC Radio Network Controller PCF Packet Control Function PDSN Packet Data Serving Node ATM Asynchronous Transfer Mode HA Home Agent AAA Authentication, Authorization and Accounting ISP Internet Service Provider Nan Wu

36 Comparison of architectures

37 Evolution

38 Comparison of architecture enodeb enodeb acts as a bridge between UE and the EPC The enodeb is also responsible for many Control Plane (CP) functions The enodeb controls and analyses radio signal level measurements carried out by the UE Nan Wu BTS & BSC & RNC Enables radio communications with mobile stations (MS) via its respective radio access system A device and software associated with a Base Station, used to register mobile phones in the cell, assign control and traffic channels, perform handoffs, and process call setup and termination The governing element in the network manages the Base Stations connected to the controller. The RNC manages radio resources and some mobility management functions, and is the point where encryption is done before user data is sent to and from the MS

39 Mobility Management Entity (MME) RNC & Packet Data Control & AAA Authentication and Security Mobility Management Managing Subscription Profile and Service Connectivity RNC control distributed into MME Packet data control evolves to MME AAA A framework for intelligently controlling access to network resources, enforcing policies, auditing usage, and providing the information needed to bill for services Nan Wu

40 Serving Gateway(S GW) Mobile Switching Center (MSC) & Packet Data Serving Node (PDSN) S GW tunnel management and switching the S GW relays the data between enodeb and P GW MSC Provides telephony switching services and controls calls. The MSC switches calls between the MS and the PSTN, and between the MS and other MSs. PDSN Connection point between the Radio Access and IP networks. Manages PPP sessions between the mobile provider's core IP network and the MS Nan Wu

41 Reference 1. L. Hanzo, T. Keller.OFDM and MC CDMA : a primer Uma Shanker Jha, Ramjee Prasad. OFDM towards fixed and mobile broadband wireless access Henrik Schulze and Chris an Lüders. Theory and applica ons of OFDM and CDMA : wideband wireless communications Hui Liu, Guoqing Li. OFDM based broadband wireless networks : design and optimization Ramjee Prasad. OFDM for wireless communications systems Sławomir Pietrzyk. OFDMA for broadband wireless access Harri Holma and Antti Toskala. LTE for UMTS: OFDMA and SC FDMA Based Radio Access John Wiley & Sons, Ltd. ISBN: Samik Ghosh, Kalyan Basu, and Sajal K. Das.What a Mesh! An Architecture for Next Generation Radio Access Networ.

42 Thank you