A new dynamic link adaptation technique based on a fuzzy inference system for hybrid multicode code division multiple access/time division multiple access wideband networking waveform of software defined radio is prop...
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A new dynamic link adaptation technique based on a fuzzy inference system for hybrid multicode code division multiple access/time division multiple access wideband networking waveform of software defined radio is proposed. A constrained optimization problem is formulated under the quality of service, signal-to-noise ratio, and throughput constraints. The optimization problem is solved using the fuzzy inference system by dynamically changing the modulation technique and the number of multicodes assigned to each user. The proposed algorithm provides maximum possible data throughput as required by the user or application by reducing the packet retransmission overhead through the use of optimum waveform parameters decided through the fuzzy inference system. A novel contribution of the proposed algorithm is that it reduces the computational complexity and thus the power consumption by restricting the throughput to the required value even if the channel conditions are fair enough to allow higher throughput. Simulation results are presented to demonstrate the effectiveness of the proposed algorithm in achieving better throughput by efficiently reducing the packet retransmissions overhead.
A number of research works have suggested a possible capacity advantage when employing direct sequence-code division multiple access (DS-cdma) instead of the more common time division multiple access option for fixed ...
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A number of research works have suggested a possible capacity advantage when employing direct sequence-code division multiple access (DS-cdma) instead of the more common time division multiple access option for fixed broadband wireless access networks operating at millimeter-waves. The choice of this multiple access scheme, which, up to now, has not been foreseen by recent WiMax (worldwide interoperability for microwave access) standards, exhibits an improved performance in terms of cochannel interference in the upstream, even though it experiences higher interference in the downstream. The present paper focuses on enhancing the bottleneck downstream performance of fixed wireless networks by proposing a methodology for controlling the signal-to-interference ratio throughout the cell, so that all subscribers meet the given interference quality-of-service specifications. This is accomplished by exploiting the properties of a combination of multirate cdma techniques. The paper describes a simple policy for code assignment, which is proved to be optimal, incorporating the effect of rain fading over multiple paths. The performance of the algorithm is tested against single code DS-cdma both under long term channel statistics (static code assignment) and under dynamic channel effects (dynamic code assignment). The first test verifies the compliance of all sector subscribers with more demanding SIR specifications, while the second yields a significant improvement in terms of resource utilization.
Future wireless communication systems require highly efficient use of radio parameters. Adaptability to changing environment conditions and to service application requirements is of great importance for the design of ...
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ISBN:
(纸本)9781424403561
Future wireless communication systems require highly efficient use of radio parameters. Adaptability to changing environment conditions and to service application requirements is of great importance for the design of link adaptation. In this paper, we consider the joint optimization of cdma radio parameters to maximize the instantaneous throughput for a bit error rate (BER) target. In order to increase the granularity of the adaptation in cdma systems, combined adaptive multicode and multilevel modulation is employed. We show that this combined adaptation additionally enhances throughput in frequency-selective environments. Optimized link adaptation requires the knowledge of the channel impulse response as well as the used receiver model. Therefore, we assume that the receiver user equipment reports to the transmitter the optimum transport format maximizing the instantaneous bit rate so that a BER target is met. Joint optimization of radio parameters is based on analytical receiver performance evaluation. We assume single user multicode cdma transmission during each time-slot. The available throughput is evaluated over frequency-selective channels for RAKE receivers and for more advanced equalizers such as joint multi-code block linear equalizers.
Multicarrier direct sequence code division multiple access (MC DS-cdma) is an attractive technique for achieving high data rate transmission. This is valid regardless of whether or not the potentially large peak-to-av...
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Multicarrier direct sequence code division multiple access (MC DS-cdma) is an attractive technique for achieving high data rate transmission. This is valid regardless of whether or not the potentially large peak-to-average power ratio (PAPR) is an important factor for its application. On the other hand, code select cdma (CS-cdma) is an attractive technique with constant amplitude transmission of multicode signal regardless of subchannels. This is achieved by introducing a code select method. In this paper, we propose a new multiple access scheme based on the combination of MC DS-cdma and CS-cdma. The proposed scheme, which we call MC CS-cdma, includes as special cases the subclasses of MC DS-cdma and CS-cdma. This paper investigates the performance of these systems over a multipath frequency selective fading channel using a RAKE receiver with maximal ratio combiner. In addition, the PAPR of the proposed system is compared with that of both MC DS-cdma and CS-cdma. Simulation results demonstrate that the proposed system provides better PAPR reduction than MC DS-cdma, at the expense of the complexity of the receiver and the number of available users. The numerical result demonstrates that the proposed system has better performance than MC DS-cdma due to the increased processing gain and time diversity gain.
To provide a near-optimal low-complexity solution to parallel multiuser scheduling in code-division multiple-access (cdma), we propose generalized selection multiuser diversity (GSMuD) schemes with multi-code channel ...
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To provide a near-optimal low-complexity solution to parallel multiuser scheduling in code-division multiple-access (cdma), we propose generalized selection multiuser diversity (GSMuD) schemes with multi-code channel assignment and analyze their performance. The proposed GSMuD (L., L) schemes rank a total of L users awaiting transmissions by their signal-to-noise ratios (SNRs) and select the L-c (1 <= L-c <= L) users with the largest absolute (or normalized) SNRs for parallel channel access, which achieve near-optimal sum rate with a low scheduling complexity. The sum and individual channel throughput rates, second order statistics, fairness, and channel access statistics of the proposed GSMuD schemes are derived, taking into account different types of generalized fading channels. Compared to the round robin (RR) scheduling without SNR ranking, the GSMuD with normalized SNR ranking achieves a substantially higher sum rate while maintaining fairness. GSMuD also significantly improves the channel access performance and the degree of fairness than selective multiuser diversity (SMuD), which selects one best user only at each time slot.
Simultaneous MAC Packet Transmission (SMPT) has recently been proposed for stabilizing the throughput over wireless links, which is one of the key challenges in providing high-quality wireless multimedia services. SMP...
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Simultaneous MAC Packet Transmission (SMPT) has recently been proposed for stabilizing the throughput over wireless links, which is one of the key challenges in providing high-quality wireless multimedia services. SMPT stabilizes the wireless link by transmitting multiple packets on multiple cdma channels in parallel in response to packet drops due to wireless link errors. These parallel packet transmissions stabilize the link layer throughput, but they also increase the interference level in a given cell of a cellular network or cluster of an ad-hoc network, which in turn reduces the number of traffic flows that can be simultaneously supported in a cell/cluster. We have recently developed an analytical framework for the class of SMPT mechanisms for a simple Bernoulli packet generation process, which does not reflect the oftentimes bursty packet generation processes encountered in real networks. In this paper we develop a generalized analytical framework for SMPT, which accommodates bursty packet traffic (and also non-bursty Bernoulli traffic). This framework expresses the system dynamics in transition probabilities for a Markov chain and calculates the effects of the interference through an iterative approach. The numerical results from our analytical framework and verifying simulations indicate that SMPT provides a significant reduction in packet loss and buffer occupancies (and delay), especially for persistent traffic bursts, in exchange for a reduced number of supported flows. Our analytical framework quantifies these system trade-offs with good accuracy and can thus be employed for resource management.
This letter evaluates the peak-to-average power ratio (PAR) performance in a space-time block coded (STBC) multicode cdma (MC-cdma) system using a selected mapping (SLM) approach. The ordinary method is to apply the S...
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This letter evaluates the peak-to-average power ratio (PAR) performance in a space-time block coded (STBC) multicode cdma (MC-cdma) system using a selected mapping (SLM) approach. The ordinary method is to apply the SLM scheme for each transmit antenna individually, while the investigated SLM-based STBC MC-cdma system selects the transmitted sequence with the lowest average PAR over all transmit antennas concurrently. SLM-based STBC MC-cdma system retrieves the side information very accurately at the expense of a slight degradation of the PAR performance, which can improve the overall detection performance of the STBC MC-cdma system in the presence of erroneous side information compared to the ordinary SLM approach.
This paper analyzes the other-cell interference of forward link channel in multicode cdma system supporting a voice and data service. In this system, voice communication can be served by a basic code and data service ...
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This paper analyzes the other-cell interference of forward link channel in multicode cdma system supporting a voice and data service. In this system, voice communication can be served by a basic code and data service can be supported by multiple codes. Using this analysis, we can get the approximated capacity of forward link. We describe the effect of data user activity and received power level ratio between a data service and a voice service. Also, this paper describes the forward link capacity and the power ratio of data power to voice power according to the change of FER threshold for data service.
A novel scheme of subband adaptive array for multicode Direct Sequence Code Division Multiple Access (DS-cdma) is proposed in this paper. The proposed scheme has a flexible configuration which allows basestation to be...
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A novel scheme of subband adaptive array for multicode Direct Sequence Code Division Multiple Access (DS-cdma) is proposed in this paper. The proposed scheme has a flexible configuration which allows basestation to be able to dynamically adapt to multirate transmission requests from subscribers. It is shown that the novel scheme can effectively suppress multiple access interferences (MAI) by appropriately forming main beam toward the desired user while pointing beampattern nulls toward MAI sources. Moreover, the combination of the subband adaptive array with the so-called cyclic prefix spreading code cdma is also proposed to mitigate multipath fading and maximize diversity gain in multipath fading environment.
multicode code division multiple access(cdma) is a promising transmission scheme for flexible and high-speed data communications. In this paper, we present a new scheme of Parallel Pilot Interference Cancellation (PPI...
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ISBN:
(纸本)7505350668
multicode code division multiple access(cdma) is a promising transmission scheme for flexible and high-speed data communications. In this paper, we present a new scheme of Parallel Pilot Interference Cancellation (PPIC) for multicode Wideband cdma system that cancels only the pilot interference of the users at the chip level practically while achieving the same performance as the standard PIC. As there is no estimation distortion in regenerating the interference, it turns out to be more robust and multi-stage process was unnecessary. Further, as the interference cancellation is processed at the chip level instead of the sample level, the complexity of interference generation could be greatly reduced which makes the implement more feasible.
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