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The uplink bandwidth request is of our main interest in this work. It may be done
in two di erent ways: polling-based (centralized) or contention-based (distributed). In
the polling scheme, the BS polls each user alternately for its intent to transmit, which
is suitable for the rtPS service [64]. In the contention scheme, users contend for the
transmission opportunity via random access, which is suitable for the nrtPS service [64].
Regardless of the scheme adopted, the bandwidth request process is completed in the
uplink section, and results are broadcasted to users through the UL-MAP messages in
the downlink. Then, users will use the uplink subchannels according to the assignment
information in UL-MAP as shown in Fig. 4.1.
We consider the contention-based uplink channel allocation in this work, which is a
distributed scheme by nature. The medium access is performed on ranging subchannels.
The available subchannels are divided into logical subgroups that correspond one-to-one
to the remaining uplink data subchannels. Thus, a user who plans to use a particular
data subchannel will contend for its usage on the corresponding ranging subchannels.
Note that a subchannel (SC) is a clustering of serveral adjacent subcarriers [54].
4.3 Proposed OARSB Scheme
The distributed uplink channel allocation for OFDMA may be performed using the slotted
Aloha scheme [14] due to the slotted structure of OFDMA. A collision resolution policy
may also be incorporated to regulate the packet retransmission as well as enhance the
throughput. Thanks to the multiband structure of OFDMA, a fast collision resolution
scheme can be performed in the frequency domain as well [30]. That is, collided packets
81
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 95 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | The uplink bandwidth request is of our main interest in this work. It may be done in two di erent ways: polling-based (centralized) or contention-based (distributed). In the polling scheme, the BS polls each user alternately for its intent to transmit, which is suitable for the rtPS service [64]. In the contention scheme, users contend for the transmission opportunity via random access, which is suitable for the nrtPS service [64]. Regardless of the scheme adopted, the bandwidth request process is completed in the uplink section, and results are broadcasted to users through the UL-MAP messages in the downlink. Then, users will use the uplink subchannels according to the assignment information in UL-MAP as shown in Fig. 4.1. We consider the contention-based uplink channel allocation in this work, which is a distributed scheme by nature. The medium access is performed on ranging subchannels. The available subchannels are divided into logical subgroups that correspond one-to-one to the remaining uplink data subchannels. Thus, a user who plans to use a particular data subchannel will contend for its usage on the corresponding ranging subchannels. Note that a subchannel (SC) is a clustering of serveral adjacent subcarriers [54]. 4.3 Proposed OARSB Scheme The distributed uplink channel allocation for OFDMA may be performed using the slotted Aloha scheme [14] due to the slotted structure of OFDMA. A collision resolution policy may also be incorporated to regulate the packet retransmission as well as enhance the throughput. Thanks to the multiband structure of OFDMA, a fast collision resolution scheme can be performed in the frequency domain as well [30]. That is, collided packets 81 |
