Channel Throughput Research Articles

Visual Entropy Gain for Wavelet Image Coding

Wavelet image coding exhibits a robust error resilience performance by utilizing a naturally layered bitstream construction over a band-limited channel. In this letter, a new measure that appears to provide a better assessment of visual entropy for comparing and evaluating progressive image coders is defined based on a visual weight over the wavelet domain. This visual weight is characterized by the human visual system (HVS) over the frequency and spatial domains and is then utilized as a criterion for determining the coding order of wavelet coefficients, resulting in improved visual quality. A transmission gain, which is expressed by visual entropy, of up to about 23% can be obtained at a normalized channel throughput of about 0.3. In accordance with the subjective visual quality, a relatively high gain can be obtained at a low channel capacity

A dynamic radio resource management technique for multiple APs in WLANs

As more and more wireless LANs are deployed in many popular locations, there is a need for dynamic radio resource management (RRM) schemes. This paper proposes a new dynamic RRM technique for multiple APs network. First, we develop a real-time algorithm to estimate the number of active stations from the standpoint of an AP, instead of a station. Second, we propose a dynamic RRM algorithm that not only significantly increases network performance but also reduces the co-channel interference. Third, we find the optimal switching probability that minimizes the transient time for an AP to reach its equilibrium state. For uniform traffic conditions, our scheme produces classical optimal frequency assignments. For non-uniform traffic conditions, it produces sub-optimal frequency assignments. Our simulations have shown that the proposed RRM technique adapts to dynamic network conditions and increases the channel throughput up to 65% in less than 20 iterations. The results can be applied to practical WLANs to significantly improve network performance

Theoretical Analysis and Performance of NC-PRMA Protocol for Multichannel Wireless Networks

In this paper, we analyze the effect of duplexing schemes on the throughput and the average packet dropping probability of a new multichannel wireless access protocol which allows for non-collision packet reservation multiple access with multiple channel (NC-PRMA/MC). N C equal-capacity, orthogonal, traffic channels are shared by M mobile users on the uplink. Transmission attempts on the uplink are made by using time-frequency signaling in every frame, which enables transmission attempts of mobile users to be conveyed to the base station without collisions. Two kinds of duplexing schemes, frequency division duplexing and shared time division duplexing, are considered in the performance analysis. Using a discrete-time Markov chain analysis, we derive the analytic expressions for the average per channel throughput and the average packet dropping probability. Computer simulation results verify the analysis. Analytical evaluation and computer simulation show that NC-PRMA/MC with shared time division duplexing improves the channel capacity, which approaches the theoretical upper bound.

Optimal ACK mechanisms of the IEEE 802.15.3 MAC for ultra-wideband systems

Ultra-wideband (UWB) transmission is an emerging wireless technology for future short-range indoor and outdoor multimedia applications. To coordinate the access to the wireless medium among the competing devices, the IEEE 802.15.3 medium access control (MAC) is proposed for short-range high-speed wireless personal area networks (WPANs) in the IEEE 802.15.3a task group. In the MAC, three acknowledgment (ACK) mechanisms are adopted during channel time allocation for error control over the error-prone wireless channel: No-ACK, Immediate-ACK (Imm-ACK), and Delayed-ACK (Dly-ACK). Frames received with errors can be retransmitted in the Imm-ACK and Dly-ACK mechanisms. However, how to optimally use these ACK mechanisms during channel time allocation is still an open issue. In this paper, we investigate how to configure the ACK mechanism parameters in order to achieve optimal throughput performance. We first formulate the throughput optimization problem for a contention-free channel time allocation under error channel condition. We then apply the three ACK mechanisms in the contention access period, to optimize the channel throughput. Simulation results demonstrate the effectiveness of our investigation.

Software Design of CDMA based MAC Scheme for Microsatellite

CDMA (Code Division Multiple Access) technology allows many users to access the medium concurrently. The store and forward (S&F) payload is to provide message relay service for terrestrial users with simple ground terminals. The widespread method of MAC (Medium Access Control) in S&F payload is ALOHA and it has poor channel throughput efficiency. This can be improved using CDMA based MAC. In this paper, two methods of code assignment namely, static & dynamic are considered. Their design methodologies and corresponding performance measures are discussed. The performance of the proposed CDMA MAC is compared with the existing ALOHA MAC and the results are presented.

A flexible MAC protocol for the integration of high- and low-quality video streams, voice and data traffic over high-speed packet switched wireless networks

In this work, we propose and evaluate mechanisms for the multiplexing and the integrated delivery of various traffic types such as video, data and voice, over a wireless cellular high-speed packet switched network. Two different scenarios are examined where the video traffic results from videoconference sessions and high-quality media playback, respectively. In both cases we focus on the uplink channel and we thoroughly investigate, by using actual MPEG-4 video streams, the system's performance under a variety of possible loads. Our goal is to achieve high-aggregate channel throughput while preserving the quality of service requirements of each traffic type.

Region-based rate control and bit allocation for wireless video transmission

In this paper, we propose a joint source-channel region-based rate control algorithm for real-time video transmissions over wireless systems. During the video transmission, the channel throughput available to the video encoder in the wireless systems is inherently variable, due to the retransmission of the error packets using the automatic repeat request (ARQ) error control. The variable data rate of the wireless system is characterized by the packet-level Gilbert two-state Markov Model, the parameters of which are extracted from the statistical properties of the channel information obtained from the wireless channel simulator. The proposed algorithm adopts a fast but effective block-based segmentation method to extract the regions of interest. Unlike traditional bit allocation methods used in the region/content-based rate control, the algorithm exploits the most effective criteria "coding qualities" as quantitative factors to directly control bit allocation among different regions so as to achieve better visual quality in the regions of interest. The computational complexity of the algorithm is low making it suitable for real-time applications. Compared with the MPEG-4 rate control algorithm, our algorithm can effectively enhance the perceptual quality for the regions of interest and significantly reduce the number of frame skipping; thereby, improve the smoothness of the video.

Frequency Reuse Power Allocation for Broadband Cellular Networks

An FRPA (frequency reuse power allocation) technique by employing the frequency reuse notion as a strategy for overcoming the ICI (intercell interference) and maintaining the QoS (quality of service) at the cell boundary is described for broadband cellular networks. In the scheme, the total bandwidth is divided into sub-bands and two different power levels are then allocated to sub-bands based on the frequency reuse for forward-link cell planning. In order to prove the effectiveness of the proposed algorithm, a Monte Carlo simulation was performed based on the Chemoff upper bound. The simulation shows that this technique can achieve a high channel throughput while maintaining the required QoS at the cell boundary.

Scheduling and Traffic Policing for Variably Demanding Video Traffic Integrated with Voice and Data Traffic in 4th Generation Wireless Networks

In this paper, we present an effective mechanism for scheduling and traffic policing in 4th generation wireless networks. More specifically, we: a) extend our previous work on a Multiple Access Control (MAC) scheme for the multiplexing of voice, video and bursty data traffic over a very high-speed wireless TDMA channel, and we study our scheme's performance when MPEG-4 videoconference users of various traffic characteristics are present in the system, and b) we combine the MAC mechanism with an improved version of an efficient traffic policing mechanism. Our results are derived for cases with and without handoff traffic in the uplink channel, and it is shown that although the burstiness of MPEG-4 traffic and channel errors impedes the maximization of channel throughput, our scheme still achieves high channel throughput for all the combined voice/video/data loads examined.

A fully dynamic scheduling mechanism for multimedia integration in next generation wireless networks

In this paper we design and study the performance of a Multiple Access Control (MAC) scheme for the multiplexing and the integrated delivery of voice, video and bursty data traffic over a high-speed wireless TDMA channel. We compare our results with a previously proposed efficient MAC protocol and we show that, regardless of the much more severe (and realistic) channel conditions examined in our work, our scheme clearly outperforms the previously proposed protocol in terms of channel throughput and voice capacity, due to the use of two novel ideas.

Joint transceiver design for MIMO communications using geometric mean decomposition

In recent years, considerable attention has been paid to the joint optimal transceiver design for multi-input multi-output (MIMO) communication systems. In this paper, we propose a joint transceiver design that combines the geometric mean decomposition (GMD) with either the conventional zero-forcing VBLAST decoder or the more recent zero-forcing dirty paper precoder (ZFDP). Our scheme decomposes a MIMO channel into multiple identical parallel subchannels, which can make it rather convenient to design modulation/demodulation and coding/decoding schemes. Moreover, we prove that our scheme is asymptotically optimal for (moderately) high SNR in terms of both channel throughput and bit error rate (BER) performance. This desirable property is not shared by any other conventional schemes. We also consider the subchannel selection issues when some of the subchannels are too poor to be useful. Our scheme can also be combined with orthogonal frequency division multiplexing (OFDM) for intersymbol interference (ISI) suppression. The effectiveness of our approaches has been validated by both theoretical analyses and numerical simulations.

Comprehensive Analysis of the IEEE 802.11

Wireless Local Area Networks (WLANs) have attracted significant research interest over the past few years. The IEEE 802.11 standard is the most mature technology for WLANs and has been widely adopted for wireless networks. This paper outlines a new performance analysis for IEEE 802.11 Distributed Coordinated Function (DCF) using Direct Sequence Spread Spectrum (DSSS) in terms of the channel throughput, packet processing rate, packet loss probability and average packet delay using a perfect channel as well as a slow Rayleigh fading channel. The theoretical results are subsequently compared with the simulation results. It is shown that there is a good match between these two results, which validates the analytical model.

Integrated Wireless Access for Videoconference From MPEG-4 and H.263 Video Coders With Voice, E-mail, and Web Traffic

In this paper, a new medium access control protocol for wireless communications, named Multimedia Integration Multiple Access Control (MI-MAC), is presented and investigated. We explore, via an extensive simulation study, the performance of MI-MAC when integrating voice, e-mail data, and web packet traffic with either MPEG-4 or H.263 videoconference streams over a noisy wireless channel of high capacity. Our scheme, one of the first in the literature that considers the integration of MPEG-4 or H.263 streams with other types of packet traffic over wireless networks, achieves high aggregate channel throughput in all cases of traffic load, while preserving the quality of service (QoS) requirements of each traffic type.

Optimal flow distribution among multiple channels with unknown capacities

Consider a simple network flow problem in which a flow of value D must be split among n channels directed from a source to a sink. The initially unknown channel capacities can be probed by attempting to send a flow of at most D units through the network. If the flow is not feasible, we are told on which channels the capacity was exceeded (binary feedback) and possibly also how many units of flow were successfully sent on these channels (throughput feedback). For throughput feedback we present optimal protocols for minimizing the number of rounds needed to find a feasible flow and for minimizing the total amount of wasted flow. For binary feedback we present an asymptotically optimal protocol.

A bandwidth reservation mechanism for prioritized multimedia integrated access with very high channel throughput in beyond 3G TDMA-based wireless networks

A Medium Access Control (MAC) protocol for mobile wireless multimedia communications is presented and investigated. The new ideas presented in the protocol are combined with well known policies from the literature and the protocol is shown to achieve very high channel throughput results, whilst preserving the strict Quality of Service (QoS) requirements for all traffic types. We evaluate, via simulations, the performance of the protocol when integrating voice, video and bursty data packet traffic over a wireless TDMA-based channel of high capacity, and we focus on the impact of different types and loads of data traffic on the system performance.

Channel states dependent fair service: a new packet scheduling algorithm for CDMA

In this paper, we address the problem of packet scheduling for high speed CDMA, which can provide high speed data service for mobile users. We first investigate the appropriate multiple access schemes in high speed CDMA. We find through mathematical analysis that TDM is more efficient than CDM for downlink in high speed CDMA networks in some general situations. Based on this finding, we propose and evaluate an efficient scheduling scheme, namely Channel States Dependent Fair Service for CDMA (CSDFSC), for packet scheduling in high speed CDMA networks. CSDFSC tries to maximize channel throughput under fairness and transmission power constraints. This scheme differentiates best-effort and guaranteed services by assigning different queue weights to various traffic classes. By considering the difference between the pre-defined and actually occupied bandwidth proportion in the priority computation, CSDFSC exhibits good fairness properties for best-effort flows. We compare the performance of CSDFSC with that of WISPER and WRR by using ns-2 simulations, where VBR video and TCP traffic flows are considered. The numerical results show that CSDFSC outperforms them in terms of throughput, link utilization and average end-to-end packet delay, while retaining a low implementation complexity.

Optimal selection of ARQ parameters in QAM channels

For a quadrature amplitude modulation (QAM) communication channel with forward error correction (FEC) and automatic repeat request (ARQ), the bit error rate (BER) is estimated as a function of the channel signal-to-noise ratio (SNR). A method is presented for trading off the number of allowed transmissions and the level of margin (or the line ARQ gain) applied to the channel SNR. The line ARQ gain maximizing the channel throughput is shown to be a sum of the channel SNR and some function of the bit load and FEC parameters. Using this result, we formulate a fast method of determining the optimum ARQ parameters at the actual channel conditions, based on their values at some reference conditions, the latter being either stored in the modem memory or pre-calculated prior to channel initialization. The derivations are presented both for AWGN and slowly fading channel conditions. Copyright © 2004 John Wiley & Sons, Ltd.

Exploiting Wireless Channel State Information for Throughput Maximization

We consider the problem of scheduling packets over channels with time-varying quality. This problem has received a lot of attention lately in the context of devising methods for providing quality of service in wireless communications. Earlier work dealing with this problem considered two cases. One case is that the arrival rate vector is in the throughput region and then policies that stabilize the system are pursued. The other case is that all packet queues are saturated and then policies that optimize an objective function of the channel throughputs are investigated. In this paper, we address the case where no assumption on the arrival rates is made. We obtain a scheduling policy that maximizes the weighted sum of channel throughputs. Under the optimal policy, in the general case, the system may operate in a regime where some queues are stable, while the other become saturated. If stability for the whole system is at all possible, it is always achieved. The optimal policy is a combination of a criterion that gives priorities based on queue lengths and a strict priority rule. The scheduling mechanism switches between the two criteria based on thresholds on the queue lengths and is modulated by the availability of the channels. The analysis of the operation of the system involves the study of a vector process which in steady state has some of its components stable while others are unstable. We adopt a novel model for time-varying channel availability that dispenses with the statistical assumptions and makes a rigorous description of system dynamics possible.

On the Throughput Enhancement of the Downstream Channel in Cellular Radio Networks Through Multihop Relaying

In this paper, we study the effect of multihop relaying on the throughput of the downstream channel in cellular networks. In particular, we compare the throughput of the multihop system with that of the conventional cellular system, demonstrating the achievable throughput improvement by the multihop relaying. We also propose a hybrid control strategy for the multihop relaying, in which we advocate the use of both, the direct transmission and the multihop relaying. Our study shows that most of the throughput gain can be obtained with the use of a two- and three-hop relaying scheme. Substantial throughput improvement could be additionally obtained by operating the concurrent relaying transmission in conjunction with the nonconcurrent transmission. We also argue here that the multihop relaying technology can be utilized for mitigating unfairness in quality-of-service (QoS), which comes about due to the location-dependent signal quality. Our results show that the multihop system can provide more even QoS over the cell area. The multihop cellular network architecture can also be utilized as a self-configuring network mechanism that efficiently accommodates variability of traffic distribution. We have studied the throughput improvement for the uniform, as well as for the nonuniform traffic distribution, and we conclude that the use of multihop relaying in cellular networks would be relatively robust to changes in the actual traffic distribution.

Multiple-Antenna Channel Hardening and Its Implications for Rate Feedback and Scheduling

Wireless data traffic is expected to grow over the next few years and the technologies that will provide data services are still being debated. One possibility is to use multiple antennas at base stations and terminals to get very high spectral efficiencies in rich scattering environments. Such multiple-input/multiple-output (MIMO) channels can then be used in conjunction with scheduling and rate-feedback algorithms to further increase channel throughput. This paper provides an analysis of the expected gains due to scheduling and bits needed for rate feedback. Our analysis requires an accurate approximation of the distribution of the MIMO channel mutual information. Because the exact distribution of the mutual information in a Rayleigh-fading environment is difficult to analyze, we prove a central limit theorem for MIMO channels with a large number of antennas. While the growth in average mutual information (capacity) of a MIMO channel with the number of antennas is well understood, it turns out that the variance of the mutual information can grow very slowly or even shrink as the number of antennas grows. We discuss implications of this "channel-hardening" result for data and voice services, scheduling, and rate feedback. We also briefly discuss the implications when shadow fading effects are included.