Contrary to real-time services, for data-centric services that are tolerant of latency, transmission with modulation and coding rates selected according to the instantaneous channel condition can increase the system t...
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Contrary to real-time services, for data-centric services that are tolerant of latency, transmission with modulation and coding rates selected according to the instantaneous channel condition can increase the system throughput. Nonetheless, the switching thresholds for using different modulation and coding schemes (MCS) highly depend on the channel and system characteristics, and are usually difficult to be determined offline. In this paper, we revisit the adaptive threshold adjustment algorithms proposed previously for adaptive modulation and coding (AMC) systems. By providing an analysis that further considers hybrid ARQ and the channel statistics, we show that the error rate conditions these algorithms use to adjust the thresholds do not necessarily reflect the actual error rates (and throughput) achieved by the MCSs. For systems or applications that have requirements on the error rates, this property is undesirable. In order to offer precise control of the error rates and guarantee that the system meets the desired performance, further conditions and modifications are derived
It is a big challenge to design an effective scheduling algorithm for multimedia transmissions over a wireless channel that employs adaptive modulation and coding (AMC). On one hand, the scheduling algorithm needs to ...
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It is a big challenge to design an effective scheduling algorithm for multimedia transmissions over a wireless channel that employs adaptive modulation and coding (AMC). On one hand, the scheduling algorithm needs to schedule user transmissions by taking advantages of the channel diversity so that the overall system performance can be improved. On the other hand, the algorithm also needs to maintain fairness among users and to provide QoS guarantee based on user requirements. In this paper, we propose a novel scheduling algorithm called QoS-based cross-layer scheduling algorithm (QoS-CLS) to address the aforementioned issues. To maximize the system throughput, the algorithm takes into consideration both the physical layer and data link layer information to schedule user transmissions. Using the cross-layer information, the scheduling problem is formulated into a Markov decision process (MDP) and the optimum decision policy (based on the channel status, traffic state and buffer status of each traffic flow) is precalculated by linear programming and stored in the system for scheduling in real-time. Results show that QoS-CLS can greatly enhance the channel throughput compared to the opportunistic scheduling algorithm because of its cross-layer QoS consideration and the optimization method. Moreover, it can provide QoS guarantee and facilitate resource sharing among different traffic flows.
Erlang capacity is traditionally defined as the maximum value of offered traffic among different service classes that the system can support when the blocking probabilities at the call admission control (CAC) level do...
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Erlang capacity is traditionally defined as the maximum value of offered traffic among different service classes that the system can support when the blocking probabilities at the call admission control (CAC) level do not exceed certain thresholds. That is valid when a fixed amount of bandwidth is allocated to each user in each frame during the whole service time. However, with the introduction of adaptive modulation and coding (AMC) scheme employed at the physical layer, outage might occur due to the fact that the allocation of bandwidth is dynamic based on the time-varying wireless channel conditions. In this paper, we evaluate the Erlang capacity of a TDMA system with AMC supporting voice and data traffics, by taking both the blocking and the outage probabilities into account. The analytical models for calculating the blocking and the outage probabilities are developed separately, and a joint algorithm for determining the Erlang capacity of the system is proposed with some numerical examples.
GSM/EDGE is the world's largest and most widespread cellular technology. EDGE offers an attractive solution for 3 rd generation cellular services in existing GSM networks. The introduction of new services into an...
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GSM/EDGE is the world's largest and most widespread cellular technology. EDGE offers an attractive solution for 3 rd generation cellular services in existing GSM networks. The introduction of new services into an existing network typically leads to increased capacity demands, since more users of different service types need to coexist in limited spectrum, while the existing speech service is required to function at least as well as before. Higher Order modulation in combination with Turbo coding is proposed to substantially enhance spectrum efficiency and average user bit rates in GSM/EDGE through improved interference robustness and increased peak bit rates. Simulation results indicate link level gains of 2.5-5.5 dB. When additionally applying incremental redundancy, similar relative improvements are shown. Bit rates can be increased by more than 30%, at C/I levels above 30dB. System performance gains are indicated by average user bit rate enhancements of up to 30-40%, along with substantial gains in spectrum efficiency, up to 40%. It is also shown that system gains are rather insensitive to frequency reuse and whether frequency hopping is applied or not (in sparse reuse scenarios).
In this paper we define and address a new problem that arises when a base station in a broadband wireless network wishes to multicast information to a large group of nodes and to guarantee some level of reliability us...
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ISBN:
(纸本)9781424435128
In this paper we define and address a new problem that arises when a base station in a broadband wireless network wishes to multicast information to a large group of nodes and to guarantee some level of reliability using Application layer FEC codes. Every data block to be multicast is translated into a sequence of K + n packets, from which every receiver must receive at least K in order to correctly decode the block. The new problem is to determine which PHY layer MCS (modulation and coding Scheme) the base station should use for each packet. We present several variants of this problem, which differ in the number of ARQ (Automatic Repeat reQuest) rounds during which the delivery of a data block must be completed. Most of these variants are shown to be NP-hard. However, we present optimal solutions for practical instances, where the number of MCSs is small, and efficient approximations and heuristics for the general case of each variant.
We propose a link adaptation technique for IEEE 802.11n MIMO-OFDM systems with convolutional coding. The technique dynamically selects the best modulation and coding scheme (MCS) based on channel conditions and on the...
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We propose a link adaptation technique for IEEE 802.11n MIMO-OFDM systems with convolutional coding. The technique dynamically selects the best modulation and coding scheme (MCS) based on channel conditions and on the medium access control (MAC) layer performance (coded BER or PER) requested by applications. We show that the coded performance at decoder output can be modeled as a function of decoder-input uncoded BER and the code rate. For MIMO-OFDM systems with different modulation types for different spatial streams at each subcarrier, we propose a simple and accurate method for computing the BER for each spatial stream mixed from different subcarriers. We also discuss approaches for searching and selecting the MCS.
A cross-layer design is developed for quality-of-service (QoS) guaranteed traffic. The proposed design jointly exploits the error-correcting capability of the truncated automatic repeat request (ARQ) protocol at the d...
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A cross-layer design is developed for quality-of-service (QoS) guaranteed traffic. The proposed design jointly exploits the error-correcting capability of the truncated automatic repeat request (ARQ) protocol at the data link layer and the adaptation ability of the adaptive modulation and coding (AMC) scheme at the physical layer to optimize the system performance. The queuing behavior induced by both the truncated ARQ protocol and the AMC scheme is analyzed with an embedded Markov chain. Analytical expressions for performance metrics such as packet loss rate, throughput and average packet delay are derived. Using these expressions, a constrained optimization problem is solved numerically to jointly determine the retry limit for the truncated ARQ protocol as well as the prescribed packet error rate for the AMC scheme so that the overall system throughput is maximized under the specified QoS constraints.
Adaptive modulation and coding scheme (AMC) is an effective way to achieve high data rate communication. In AMC system, the key issue is to determine the switching rule for different modulation and coding scheme (MCS)...
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Adaptive modulation and coding scheme (AMC) is an effective way to achieve high data rate communication. In AMC system, the key issue is to determine the switching rule for different modulation and coding scheme (MCS). In this paper, adaptive threshold controlling scheme for AMC is proposed. The proposed scheme controls switching thresholds according to target block error rate. Simulation results have shown that the throughput performance of the proposed scheme is very close to the performance, which obtained by the optimum SIR thresholds.
Due to the time variant characteristic of wireless communication channels, channel-state-information (CSI) becomes out-of-date if we consider the CSI feedback delay. Thus, channel prediction is required to mitigate th...
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Due to the time variant characteristic of wireless communication channels, channel-state-information (CSI) becomes out-of-date if we consider the CSI feedback delay. Thus, channel prediction is required to mitigate this phenomenon. In this paper, we propose an adaptive modulation and coding (AMC) scheme using channel prediction on multipath Rayleigh fading channels and evaluate the performance of the proposed scheme. For a given modulation and coding set (MCS), the average packet error rates are derived as functions of the predicted channel information and the prediction error variance. Based on CSI's, the required transmit power is obtained for each MCS option, simulation results show that the performance degradation due to feedback delay can be compensated by the proposed scheme
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