We consider the joint exploitation of coding and diversity techniques to achieve efficient, reliable wireless transmission. The system of interest comprises a powerful non-binary low-density parity-check (LDPC) code t...
详细信息
We consider the joint exploitation of coding and diversity techniques to achieve efficient, reliable wireless transmission. The system of interest comprises a powerful non-binary low-density parity-check (LDPC) code that will be soft-decoded to supply strong error protection, a quadratic amplitude modulator (QAM) that directly takes in the non-binary LDPC symbols and will be soft-demodulated, and a modulation diversity (or signal space diversity, SSD) operator that will provide power- and bandwidth-efficient diversity gain. By relaxing the rate of the SSD rotation matrices to below 1, we show that a better rate allocation can be arranged between the LDPC codes and the SSD, which brings significant performance gain over previous systems. To facilitate the design and evaluation of the relaxed SSD rotation matrices, three types of efficient constructions are demonstrated and a set of four criteria are developed. Through analysis and simulations, we show that our strategies are very effective in combating random fading and strong noise on Rayleigh fading channels.
Multipulse pulse position modulation (MPPM) has been widely proposed to improve data rate over the traditional pulse position modulation (PPM) in free-space optical communication systems. However, there is no known ef...
详细信息
ISBN:
(纸本)9781424457090;9781424457113
Multipulse pulse position modulation (MPPM) has been widely proposed to improve data rate over the traditional pulse position modulation (PPM) in free-space optical communication systems. However, there is no known efficient method of encoding MPPM codewords. Furthermore, MPPM is not the optimal coding scheme (in terms of data rate) given the two main constraints of optical systems (duty cycle and zero runlength). In this paper, a new coding technique based on constrained coding is introduced that allows construction of codes which achieve considerable rate gain over comparable MPPM systems. In addition, our new codes allow for convenient concatenation with an outer code and are suitable for iterative decoding. Simulation results show that these codes can achieve a 6 dB coding gain over comparable MPPM systems.
The downlink of the Long Term Evolution (LTE) would be OFDMA based and combination of Hybrid ARQ at the data link layer with adaptive modulation and coding (AMC) at the physical layer might be employed. Constellation ...
详细信息
ISBN:
(纸本)9781424463275;9780769539898
The downlink of the Long Term Evolution (LTE) would be OFDMA based and combination of Hybrid ARQ at the data link layer with adaptive modulation and coding (AMC) at the physical layer might be employed. Constellation rearrangement (CR) technique is used in HARQ to enhance MQAM performance. An improved mapping method is used in full IR to enhance system performance. An improved SNR estimation algorithm which reduces computational time is applied to get CQI and corresponding modulation and coding scheme is chosen to maximize throughput performance. Simulation results show that the joint design of AMC and HARQ can achieve considerable spectral efficiency gain.
A new hybrid digital/analog scheme is proposed for lossy transmission of a Gaussian source over a two-receiver bandwidth-matched Gaussian broadcast channel with source side information available at each receiver. The ...
详细信息
A new hybrid digital/analog scheme is proposed for lossy transmission of a Gaussian source over a two-receiver bandwidth-matched Gaussian broadcast channel with source side information available at each receiver. The proposed scheme makes use of a new level of freedom for point-to-point transmission and combines two previously known schemes that are optimal under two different conditions regarding channel and side information quality parameters. It is shown that for the entire intermediate region in the parameter space sandwiched between those two conditions, the proposed scheme can achieve the same distortion-power tradeoff as in point-to-point transmission simultaneously for both channels, and is therefore optimal.
High demand for mobile voice puts forth the requirement of high VoIP capacity over WiMAX networks. Although WiMAX networks are well-known for high-speed internet access on the go, VoIP capacity over WiMAX is low due t...
详细信息
High demand for mobile voice puts forth the requirement of high VoIP capacity over WiMAX networks. Although WiMAX networks are well-known for high-speed internet access on the go, VoIP capacity over WiMAX is low due to large control overhead. In this paper, we propose Group Resource Allocation (GRA) mechanism that reduces the control overhead and hence increases VoIP Capacity over WiMAX. In GRA multiple users are provided allocation as a group. Grouping is based on common traffic and channel characteristics and uses bitmaps to signal resource allocation information to users. Grouping of users and use of bitmaps reduces control overhead. Simulation results show that a 40% gain in VoIP capacity over WiMAX can be achieved with Group Resource Allocation.
We propose a Dynamic Hybrid Scheduler (DHS) for Mobile Broadband Wireless Systems composed by two basic components, corresponding to a guaranteed and a dynamic delay based rate allocation policy respectively. The prop...
详细信息
We propose a Dynamic Hybrid Scheduler (DHS) for Mobile Broadband Wireless Systems composed by two basic components, corresponding to a guaranteed and a dynamic delay based rate allocation policy respectively. The proposed scheduler is balanced between these two scheduling disciplines and thus combines their merits in an effective manner. Furthermore, a delay bound is obtained for each service under the assumptions of (a) reliable channel conditions and (b) employment of the least power demanding coding and modulation scheme. DHS is applicable to various Mobile Broadband Wireless Systems such as HSPA, 1xEVDO and Mobile WiMAX and its performance is evaluated through event driven simulation and compared against another delay driven scheduler namely Feasible Earliest Due Date (FEDD) a variation of classic EDD modified for wireless systems.
So far, many researches on network coding are performed with higher layer protocols such as MAC, routing, and flow control protocols without consideration of physical layer issues such as channel conditions of links. ...
详细信息
So far, many researches on network coding are performed with higher layer protocols such as MAC, routing, and flow control protocols without consideration of physical layer issues such as channel conditions of links. However, in wireless networks, the consideration of properties at the physical layer is important to improve system performance. Hence, in this paper, we study an opportunistic scheduling and adaptive modulation problem for wireless networks with network coding, which is a joint problem for MAC and physical layers. A similar problem was studied in considering an idealized system in which the data rate of each link is modeled with the Shannon capacity. They showed that to maximize the throughput of a transmission, the optimal subset of native packets that are encoded within a coded packet should be selected based on the channel condition at the destination for each native packet. Moreover, they also showed that it may not be the optimal selection to encode all possible native packets within a coded packet. In this paper, we consider a more realistic model than that of with practical modulation schemes such as M-PSK and MQAM. We show that the optimal policy that maximizes the throughput of a transmission is to encode all available native packets within a coded packet regardless of the channel condition at the destination for each native packet, which is a different conclusion from that of. However, we show that adaptive modulation, in which its constellation size in a coded packet is adjusted based on the channel condition of each destination node, provides a higher throughput than the scheme with fixed modulation, in which its constellation size is always fixed regardless of the channel condition at each destination node.
We consider a link adaptation scheme with adaptive coding and modulation and adaptive retransmissions on a block fading channel. Therefore, we characterize the performance of the employed channel code with puncturing ...
详细信息
We consider a link adaptation scheme with adaptive coding and modulation and adaptive retransmissions on a block fading channel. Therefore, we characterize the performance of the employed channel code with puncturing and repetition coding in a unified way and use this description to devise a method to adapt modulation and code rate in the initial transmission as well as in all retransmissions. We evaluate the performance of two adaptation strategies and compare them to the throughput-optimum and a simple scheme with fixed-length retransmissions.
IEEE 802.16e-based Mobile WiMAX has gained considerable popularity recently. However, there is no current simulation model that provides feature completeness and performance accuracy. In this paper we propose the desi...
详细信息
IEEE 802.16e-based Mobile WiMAX has gained considerable popularity recently. However, there is no current simulation model that provides feature completeness and performance accuracy. In this paper we propose the design and implementation methodology of a complete, accurate, realistic and versatile simulation model to support Mobile WiMAX for the NS-2 simulation platform. In the proposed simulation model design, all major mandatory as well as many optional features in the IEEE 802.16e standard are implemented based on the enhancement of an open-source WiMAX model published by NIST. The major contributions of this work are: 1) the additional features integrated to the NIST model including OFDMA physical layer, 2) periodical ranging and Adaptive modulation and coding (AMC) for robust link adaptation, 3) multi-hop support for large-scale test-bed simulation, as well as 4) the simulation model validation using WiMAX Forum certified devices. Versatile simulation scenarios are also designed to validate the implemented features.
Permutation codes are used in powerline communications (PLC), together with M-FSK modulation, to combat errors introduced by the channel. Synchronization errors are rare but can be catastrophic if not detected and cor...
详细信息
Permutation codes are used in powerline communications (PLC), together with M-FSK modulation, to combat errors introduced by the channel. Synchronization errors are rare but can be catastrophic if not detected and corrected. In this paper, we propose a fast and simple decoding algorithm that uses a tree structure, called a permutation code tree, to detect and correct errors. The decoder is able to detect and correct substitution, insertion or deletion errors. The decoder has an error correction capability of one error per codeword.
暂无评论