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4.5 Simulation Results
Computer simulation is performed in this section to demonstrate the performance of
the proposed OARSB scheme and verify the analysis given in Sec. 4.4 numerically. An
OFDMA system is implemented with parameters speci ed in [94]. We choose an FFT
size of 512, which is divided into 16 subchannels, each of which has 32 subcarriers. One
subchannel is dedicated for the ranging purpose. Thus, we have M = 15 data subchan-
nels for contention. The Rayleigh fading channel is adopted in the simulation and its
parameters are chosen such that the assumption A1 in Sec. 4.4 is met.
The throughput performance of the proposed OARSB scheme is shown in Figs. 4.5 and
4.6 for K = 3 and 5, respectively, with the OMC-Aloha scheme [14] as the performance
benchmark. Both schemes allow an equal number of requested (active) subchannels, L,
from each user for fair comparison. W = 3 is considered for the OARSB scheme. We see
that the throughput of both schemes is lower when L is too small or too big due to low
channel utilization and intense collision, respectively. The best throughput is achieved
around operational points of L = M=K or M=K 1. It is observed that the adoption
of collision resolution in OARSB greatly improves its throughput for the region centered
around operational points. This can be explained by the fact that random subchannel
backo judiciously switches to other subchannels so that collision is e ciently resolved
among users. Moreover, OARSB gives a higher priority to better subchannels so that
multiuser diversity is exploited accordingly.
Figs. 4.5 and 4.6 compare the analytical and simulation results. We see that they agree
well for L M=K, which is the typical operational region. However, the discrepency
96
Object Description
| Title | Resource allocation in OFDM/OFDMA cellular networks: protocol design and performance analysis |
| Author | Chang, Yu-Jung |
| Author email | yujungc@usc.edu; yjrchang@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Electrical Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2008-09-09 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-29 |
| Advisor (committee chair) | Kuo, C.-C. Jay |
| Advisor (committee member) |
Neely, Michael J. Govindan, Ramesh |
| Abstract | Orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) are two promising technologies adopted in the IEEE 802.16 standard to support broadband wireless access as well as multimedia quality-of-service (QoS). In this dissertation, we discuss several important topics regarding OFDM/OFDMA: cross-layer performance analysis of OFDM and OFDMA downlinks in terms of several QoS metrics; the medium access control (MAC) protocol design for the OFDMA uplink; and the inter-cell interference (ICI) management in multi-cell OFDMA networks through a systematic approach.; First, performance analysis of OFDM-TDMA and OFDMA networks is performed in terms of cross-layer QoS measures which include the bit rate and the bit error rate (BER) in the physical layer, and packet average throughput/delay and packet maximum delay in the link layer. We adopt a cross-layer QoS framework similar to that in IEEE 802.16, where service classification, flow control and opportunistic scheduling with different subcarrier/bit allocation schemes are implemented. Our analysis provides important insights into the performance differences of these two multiaccess systems. In addition, it is shown by analysis and simulation that OFDMA outperforms OFDM-TDMA in QoS metrics of interest. Thus, we conclude that OFDMA has higher potential in supporting multimedia services.; Second, a distributed MAC algorithm for uplink OFDMA networks under the IEEE 802.16 framework is proposed and analyzed. We present a simple yet efficient algorithm to enhance the system throughput by integrating opportunistic medium access and collision resolution through random subchannel backoff. Consequently, the resulting algorithm is called the opportunistic access with random subchannel backoff (OARSB) scheme. OARSB not only achieves distributed coordination among users but also reduces the amount of information exchange between the base station and users. The throughput and delay performance analysis of OARSB is conducted, and the superior performance of OARSB over an existing scheme is demonstrated by analysis as well as computer simulation. Besides, the proposed OARSB scheme can be easily implemented in 802.16 due to its simplicity.; Lastly, a practical and low-complexity multi-cell OFDMA downlink channel assignment method using a graphic framework is proposed. Our solution consists of two phases: 1) a coarse-scale inter-cell interference (ICI) management scheme and 2) a fine-scale channel-aware resource allocation scheme. In the first phase, the task of managing the performance-limiting ICI in cellular networks is accomplished by a graphic approach, in which no ICI measurement is needed and state-of-the-art ICI management schemes such as ICI coordination (ICIC) and base station cooperation (BSC) can be incorporated easily. In the second phase, channel assignment is accomplished by taking instantaneous channel conditions into account. Heuristic algorithms are proposed to solve both phases of the problem efficiently. Extensive simulation is conducted for various practical scenarios to demonstrate the superior performance of the proposed solution against the conventional OFDMA allocation scheme. Thanks to its practicality and low complexity, the proposed scheme can be used in next generation cellular systems such as the 3GPP Long Term Evolution (LTE) and IEEE 802.16m. |
| Keyword | OFDM; OFDMA; MAC protocol design; performance analysis; resource allocation; interference management; IEEE 802.16; cellular networks |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1704 |
| Contributing entity | University of Southern California |
| Rights | Chang, Yu-Jung |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Chang-2392 |
| Archival file | uscthesesreloadpub_Volume40/etd-Chang-2392.pdf |
Description
| Title | Page 110 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 4.5 Simulation Results Computer simulation is performed in this section to demonstrate the performance of the proposed OARSB scheme and verify the analysis given in Sec. 4.4 numerically. An OFDMA system is implemented with parameters speci ed in [94]. We choose an FFT size of 512, which is divided into 16 subchannels, each of which has 32 subcarriers. One subchannel is dedicated for the ranging purpose. Thus, we have M = 15 data subchan- nels for contention. The Rayleigh fading channel is adopted in the simulation and its parameters are chosen such that the assumption A1 in Sec. 4.4 is met. The throughput performance of the proposed OARSB scheme is shown in Figs. 4.5 and 4.6 for K = 3 and 5, respectively, with the OMC-Aloha scheme [14] as the performance benchmark. Both schemes allow an equal number of requested (active) subchannels, L, from each user for fair comparison. W = 3 is considered for the OARSB scheme. We see that the throughput of both schemes is lower when L is too small or too big due to low channel utilization and intense collision, respectively. The best throughput is achieved around operational points of L = M=K or M=K 1. It is observed that the adoption of collision resolution in OARSB greatly improves its throughput for the region centered around operational points. This can be explained by the fact that random subchannel backo judiciously switches to other subchannels so that collision is e ciently resolved among users. Moreover, OARSB gives a higher priority to better subchannels so that multiuser diversity is exploited accordingly. Figs. 4.5 and 4.6 compare the analytical and simulation results. We see that they agree well for L M=K, which is the typical operational region. However, the discrepency 96 |
