Bian, YQ., Nix, AR., Sun, Y., & Strauch, P. (2007). Performance evaluation of mobile WiMAX with MIMO and relay extensions. In IEEE Wireless Communications and Networking Conference, 2007 (WCNC 2007), Kowloon (pp. 1814 - 1819). Institute of Electrical and Electronics Engineers (IEEE). https://doi.org/10.1109/WCNC.2007.341 Peer reviewed version Link to published version (if available): 10.1109/WCNC.2007.341 Link to publication record in Explore Bristol Research PDF-document University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/red/research-policy/pure/user-guides/ebr-terms/ This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2007 proceedings. Performance Evaluation of Mobile WiMAX with MIMO and Relay Extensions Y. Q. Bian and A. R. Nix Y. Sun and P. Strauch Centre for Communications Research (CCR), Toshiba Research Europe Limited (TREL), University of Bristol, Woodland Rd, 32 Queen Square, Bristol, BS8 1UB, UK Bristol BS1 4ND Email: {y.q.bian;andy.nix}@bristol.ac.uk Email: {Sun; Paul.Strauch}@toshiba-trel.com Abstract-The latest mobile WiMAX standard promises to de- The WiMAX forum has proposed a number of profiles; these liver high data rates over extensive areas and to large user den- cover 5, 7, 8.75 and 10MHz channel bandwidths for operation sities. More specifically, data rates are expected to exceed those in worldwide licensed bands at 2.3, 2.5, 3.3 and 3.5GHz [3]. of conventional cellular technologies. The IEEE 802.16e Wi- MAX standard enables the deployment of metropolitan area In a practical urban environment, the radio channel linking networks to mobile terminals in non-line-of-sight radio envi- the BS to the MS is unpredictable and depends on the specific ronments. Current concerns include leveraging high data rates, application scenario. However, for mobile applications LoS is increasing area coverage, and competing with beyond 3G net- rarely achieved. Multiple-Input Multiple-Output (MIMO) works. Based on the IEEE 802.16e wirelessMAN-OFDMA (Or- systems have the ability to exploit NLoS channels, and hence thogonal Frequency Division Multiple Access) physical (PHY) increase spectral efficiency compared to a Single-Input Sin- layer air-interface, this paper presents a physical layer study of gle-Output (SISO) system. MIMO advantages include diver- MIMO enabled mobile WiMAX in an urban environment. The sity gains, multiplexing gains, interference suppression, and radio channels are based on those developed in the European array gains. Mobile WiMAX supports a full range of smart Union IST-WINNER project. Results are given in terms of sys- antenna technologies, including Space Time Block Codes tem throughput and outage probability with and without relays (STBC), Spatial Multiplexing (SM), and beamforming. for a range of SISO, MISO and MIMO architectures. Results MIMO is seen as a critical component in future developments show that satisfactory performance cannot be achieved in mac- of mobile WiMAX. Suitable MIMO orientated link adaptation rocells unless radio relays are used in combination with MIMO- strategies are critical to exploit the wide of range of MIMO STBC. systems and channel conditions [4]. For example, STBC of- Keywords-IEEE802.16e, WiMAX, MIMO, diversity, link fers diversity gain, but cannot improve capacity without the adaptation, relays use of Adaptive Modulation and Coding (AMC). SM com- bined with higher order modulation schemes can increase the I. INTRODUCTION peak throughput, but such schemes require extremely high SNR levels [4]. In practical urban cells it will be difficult to WiMAX (Worldwide Interoperability for Microwave Ac- exploit SM at the cell edge. The inclusion of MIMO tech- cess) is central to a number of new market and technology niques alongside flexible sub-channelization and AMC en- opportunities. The standard offers a range of broadband wire- ables Mobile WiMAX technology to improve system cover- less technologies that are capable of delivering differentiated age and capacity. Importantly, if correctly configured, these and optimized service models. WiMAX promises to combine benefits will be achieved using power and spectrum efficient high capacity services with wide area coverage. However, terminals. issues such as power and spectral efficiency still need to be resolved. In 2004, the IEEE 802.16d standard [1] was pub- The implementation and application of MIMO in a mobile lished for Fixed Wireless Access (FWA) applications. In De- WiMAX application requires further research to achieve an cember 2005 the IEEE ratified the 802.16e [2] amendment, efficient and cost-effective solution. Furthermore, coverage is which aimed to support Mobile Wireless Access (MWA) with still a key issue for mobile WiMAX users, with desired oper- seamless network coverage. This standard is now receiving ating ranges of 1.5 km per cell. It is well-known that radio considerable industrial attention. relays can be deployed to enhance coverage (and in some cases capacity) [5][6]. The mobile WiMAX air interface adopts Scalable Orthogo- nal Frequency Division Multiple Access (SOFDMA) for im- This paper focuses on the above challenges, and includes a proved multipath performance in non-line-of-sight (NLoS) comprehensive study of MIMO enabled mobile WiMAX with environments. SOFDMA provides additional resource alloca- and without the use of radio relays. The paper provides a nu- tion flexibility. 802.16e transmits using a group of sub- merical analysis of the capacity and coverage expected for channels (the number of which can be varied), and these can urban deployments. The work places specific emphasis on the be adaptively optimized to maximize performance. Spectrum downlink (DL). The limitations of WiMAX without the use of resources can be adapted to densely or sparsely populated MIMO are first identified, and the advantages of STBC and regions, making it suitable for urban or rural FWA and MWA. SM in combination with OFDMA are then evaluated. The use 1525-3511/07/$25.00 ©2007 IEEE 1816 This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the WCNC 2007 proceedings. of AMC (switching from QPSK to 64-QAM) is considered to Logical channel maximize the throughput of each individual link. Results are shown in terms of throughput, coverage and spectral effi- ciency for urban microcells and macrocells, as defined by Cha-4 Cha-2 Cha-3 Cha-1 Cha-0 pilot 3GPP2 [7]. The channel models developed within the Euro- 0~ DC (#256) 467~ 45 Physical channel pean Union IST-WINNER [8] project are used. A general 511 relay concept and deployment is also presented for coverage 00 11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424 2525 2626 2727 2828 2929 and capacity enhancement at the cell edges. 14 carriers Freq. (512 carriers) Figure 1. OFDMA air interface The remainder of this paper is organized as follows. Section II briefly describes the mobile WiMAX system profile. Sec- Fig. 1 illustrates the structure of the OFDMA symbol cluster tion III presents performance results using the WINNER on the DL. Within an OFDMA symbol, a total of 30 physical channel models for urban microcell and macrocell environ- clusters (or 15 sub-channels) are mapped (after renumbering ments. Throughput, coverage and spectrum efficiency results and permutation of the logical clusters) as specified in [2]. are presented and analyzed in section IV. Finally, the paper Each sub-channel has 24 data carriers and 4 pilot carriers. The ends with a set of conclusions. 15 sub-channels are assigned to three segments and allocated to three sectors within a cell. Hence up to 15 users can be sup- ported. A frequency reuse factor of 1 is assumed between sec- II. MIMO WIMAX: SYSTEM DESCRIPTION tors to satisfy our reliability, coverage and capacity require- The mobile WiMAX system makes use of the wireless- ments. MAN-OFDMA air interface. In essence, the principle of OFDMA consists of different users sharing the Fast Fourier The use of AMC allows the system to adjust the channel Transform (FFT) space. The architecture is based on a scal- modulation and coding scheme in sympathy with the SNR of able sub-channelization structure with variable FFT sizes ac- the link. For high SNR values, the system will select its high- cording to the channel bandwidth. With flexible channeliza- est throughput scheme (e.g., ¾ rate 64-QAM). As mentioned tion, each user may be assigned one or more sub-channels, previously, MIMO techniques are also applied in the form of and several users may transmit simultaneously in each time- SM and STBC. The link throughput for each user is calculated slot. Initial profiles under development in the WiMAX Forum from the Packet Error Rate (PER) as follows: = × − N D Nb RFEC RSTC Technical Working Group for release-1 specify bandwidths of Cthroughput D (1 PER) , where D = repre- 5 and 10MHz, with an FFT size of 512 and 1024 [3]. Ts sents the transmission date rate, and ND, Nb, RFEC, RSTC and Ts The great advantage of OFDMA is its tolerance to multipath denote the number of assigned data subcarriers, bits per sub- propagation and frequency selective fading in a mobile envi- carrier, FEC coding rate, space-time coding rate and the ronment. The use of a Cyclic Prefix (CP) can completely OFDMA symbol duration of the user. eliminate Inter Symbol Interference (ISI) so long as its dura- tion is longer than the maximum channel delay spread. Table III. APPLICATION ENVIRONMENT AND CONDITIONS 1 lists the FFT parameters for a 512-FFT OFDMA system using 5MHz of bandwidth.