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In this chapter we proposed a scheduling algorithm that maximizes the spectral efficiency while reducing the feedback load. The algorithm, called joint polling and contention based feedback (JPCF) algorithm, collects channel quality information of the users either in a polling form or in a contention form. Compared to the optimal (full feedback) algorithm, the JPCF algorithm has a similar spectral efficiency and a higher system capacity, which takes into account the effect of the feedback rate. Also, the JPCF algorithm shows more reduction in feedback load compared to the DSMUDiv algorithm. One drawback of the JPCF algorithm is the high delay compared to the DSMUDiv algorithm as the average SNR decreases, which affects the performance. As the average SNR increases, the delay encountered when using the JPCF algorithm drops below the delay created by using the DSMUDiv algorithm, which improves the system performance. The work presented in this paper includes analysis of the JPCF algorithm under slow Rayleigh fading assumption. Closed-form expressions of the feedback load, system capacity and scheduling delay are also presented in this paper. Modulation Level BPSK 4-QAM 16-QAM 64-QAM Switching Threshold (dB) th = 4.8

In this paper, we propose a scheduling algorithm that reduces the feedback load and guard time requirements for adaptive modulation multi-carrier systems. Instead of fixing a probing threshold in a polling-based system, we vary the probing threshold and allow users to feed back quantized information indicating their channel's state. The probing threshold starts with the system's minimum threshold level and increases towards the system's maximum depending on the number of employed modulation levels and the users' channel state information. Numerical results show that the proposed algorithm reduces the feedback load and the guard-time requirements with a slight penalty loss in the spectral efficiency when compared to the optimal algorithm (full feedback). Furthermore, we study the effect of our algorithm on the probability of access, system throughput and scheduling delay after deriving closed-form expressions for the feedback load and the spectral efficiency.

In this paper, we propose a reduced feedback opportunistic scheduling (RFOS) algorithm that reduces the feedback load while preserving the performance of opportunistic scheduling (OS). The RFOS algorithm is a modified version of our previously proposed algorithm, the DSMUDiv algorithm. The main difference is that RFOS consists of a probing process (search process) and a requesting feedback process based on a threshold. The threshold value is variable, and it depends on the probing process. To reduce the feedback rate, a quantised value indicating the modulation level is fed back, instead of the full value of the signal-to-noise ratio (SNR), which we call quantised SNR. The paper includes the closed-form expressions of the probing load, feedback load and spectral efficiency. In addition, we investigate the effect of the scheduling delay on the system throughput (STH). Under slow Rayleigh fading assumption, we compare RFOS algorithm with the DSMUDiv and optimal (full feedback load) selective diversity scheduling algorithms. Copyright © 2010 John Wiley & Sons, Ltd.

In this paper, we propose a scheduling algorithm that reduces the feedback load with no penalty loss in the spectral efficiency when compared to the optimal selective diversity scheme (Harthi et al. in IEEE Trans Wirel Commun 6(1), 2007). In order to reduce the feedback rate, a two stage probing technique is introduced. In the first stage, the scheduler estimates the threshold level in which the best user is likely to be found. In the second stage, the scheduler permits two users to contend for a mini-slot using only one bit of feedback information per user. After deriving closed-form expressions for the feedback load, we compare the performance of our algorithm with the discrete rate switch-based multiuser diversity (DSMUDiv) scheme (Harthi et al. in IEEE Trans Wirel Commun 6(1), 2007) and the optimal selective diversity scheme. Numerical results show that our scheme further reduces the feedback load, rate and guard time when compared to both the DSMUDiv and the optimal selective diversity schemes under slow Rayleigh fading assumption.

In this paper, we investigate the performance of a blind adaptive modulation scheme that does not require any channel knowledge and just uses binary feedback, thereby decreasing feedback load. Retransmission of erroneous packet is not considered. In particular, we present an analytical framework for the performance evaluation of a simple wireless system in terms of receiver and transmitter structure. The system requires no knowledge of the channel and relies on a binary feedback. Slow and fast Rayleigh fading channel conditions are considered. The paper includes the derivation of the closed-form expressions of the spectral efficiency. In some cases, closed-form expression for packet error rate (PER) are derived. Our results show relatively high PER but some applications can still operate in a satisfactory fashion in these conditions, such as voice communication. Using coded modulation with high coding gain and increasing the number of blocks per time slot decrease the PER even more. An advantage of this system is that it uses a low complexity receiver, which sends binary feedback. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper, we extend the results of [12] by proposing a joint polling and contention scheduling scheme that reduces the feedback load in orthogonal frequency division multiple access (OFDMA) systems employing adaptive modulation. This feedback reduction is achieved by grouping users into categories, and requesting feedback from users that belong to a certain category only. The feedback process comprises of two modes. The first mode is a polling only mode and the second mode consists of a contention stage followed by a polling stage. The contention stage is used to find the i-th category where the best user is likely to be found. All users belonging to that category are polled sequentially until an acceptable user with channel quality above a predefined threshold is found. Numerical results show that the proposed scheme reduces the feedback load and the guard-time without any loss in the spectral efficiency when compared to the optimal selective diversity with full feedback algorithm shown in [11]. We, further, derive closed-form expressions for the feedback load, average guard time and the spectral efficiency and show that the proposed scheme improves the system spectral efficiency, the feedback load and the average guard time when compared to the schemes proposed in [12].

In this work, a new lattice based algorithm for blind equalization is developed. The proposed algorithm is a generalized version of an existing lattice-based soft constraint satisfaction multi-modulus algorithm (L-SCS-MMA) and is named as lattice-based soft constraint satisfaction multi-modulus algorithm of order p (L-SCS-MMA-p). Moreover, a slicer output has been incorparated in the blind estimate of the SCS-MMA algorithm to enhance more the convergence speed of the the algorithm, and the resulting algorithm is named as (LDA-SCS-MMA-p). The performance of the proposed algorithm is investigated under different scenarios.

One of the most promising approaches to boost the communication efficiency in wireless systems is the use of multiuser diversity (MUDiv), where the fading of channels is exploited. The mechanism of scheduling the user with the best channel condition is called opportunistic scheduling (OS). In this paper we propose a joint polling and contention based feedback (JPCF) algorithm that exploits MUDiv while reducing the feedback load. The guard time, which is between bursts, is divided into minislots that alternate between polling-based feedback minislot (p-minislot) and contention-based feedback minislot (c-minislot). During the minislot, users feedback their channel qualities if above a predetermined threshold. We analyze the scheduling algorithm under slow Rayleigh fading assumption and derive the closed-form expressions of the feedback load as well as the system capacity. We also consider the delay resulting from the time needed to schedule a user and derive the system throughput. The scheduling algorithm is compared with other scheduling algorithms.

In this paper, we analytically analyze the performance of a path selection diversity scheme for downlink packet delivery. In the scheme, the scheduled user, where scheduling is based on First In First Out (FIFO) queueing systems, tries to select the best end-to-end path quality among L possible relays including his downlink channel for packet delivery. In this system communication between users is limited to a signal-hop. The scheduled packet is delivered either directly on the downlink channel or through one user (relay). Closed-form expressions of the average spectral efficiency (ASE), the probability of packet drop, and the probability of relaying is presented. We compare the path selection scheme under slow Rayleigh fading assumption with the non-selection scheme (downlink transmission).

Orthogonal frequency division multiplexing (OFDM) is emerging as a key modulation scheme for future high speed packets based wireless transmission systems. In a wireless multiuser network system, when an opportunistic scheduling is employed in the OFDM system with adaptive modulation, it may encounter implementation problems due to the need for a large amount of channel information. In this paper we propose a decentralized scheduling scheme to exploit multiuser diversity (MUDiv) in OFDM systems. Users access the channel using a simple variation of the ALOHA random access protocol, termed channel-aware/collision-limited ALOHA. Based on the channel quality, users randomly transmit a request packet with a probability p. When a collision occurs, collided users will retransmit a request packet with probability p. We present an analytical analysis of the average system throughput (average spectral efficiency). We compare our proposed scheduling scheme with the proposed scheduling scheme , the optimal selective diversity scheduling scheme (centralized scheduling), and the round-robin scheduling scheme.

Infostations is a new system concept that has been proposed to provide convenient and cost effective access to high date rate mobile data services. An efficient IP packet transmission protocol is required to compensate for the high error rate inherent to fading radio channels. In this paper we propose to investigate the performance of a selective re- peat automatic-repeat-request (SR-ARQ) scheme combined with adaptive modulation and Maximum Ratio Combining (MRC) to transfer fragmented large multimedia files over Infostations networks. Based on the channel state information (CSI), the modulation level can be switched dynamically. We will consider two access options: (i) sit-through access, and (ii) drive-through access. Closed-form expressions and computer simulations will be provided to evaluate the performance of the system.

Orthogonal frequency division multiplexing (OFDM) is emerging as a key modulation scheme for future high speed packets based wireless transmission systems. In a wireless multiuser network system, when an opportunistic scheduling is employed in the OFDM system with adaptive modulation, it may encounter implementation problems due to the need for a large amount of channel information. In this paper, we adopt an idea that we proposed in (1) called discrete rate switch-based multi-user diversity system (DSMUDiv) and combine it with the idea of Enhanced Equal Access scheduling policy that was proposed in (2) to reduces the feedback load and guarantee high probability of access for each user while maintaining most of the performance of opportunistic scheduling. We present an analytical analysis of the feedback load, spectral efficiency and probability of access of the proposed scheme.

In this paper, we propose an optimal discrete rate switch-based multiuser diversity (DSMUDiv) scheduling scheme that reduces the feedback load while preserving most of the performance of opportunistic scheduling. In order to reduce the feedback rate, quantized values indicating the modulation level are feedback instead of the full values of the SNRs (quantized SNRs). We examine the DSMUDiv scheme using two scheduling criteria depending on the distribution of the mobile users in the cell: (i) absolute signal-to-noise ratio (SNR)-based scheduling in the case of independent and identical distributed (i.i.d.) users, and (ii) normalized SNR-based scheduling in the case of i.-non-i.d. users. The paper includes the derivation of closed-form expressions of the feedback load, spectral efficiency and probability of access. Monte Carlo simulation is used to evaluate the spectral efficiency in the case of normalized SNR-based scheduling. We compare our scheduling scheme under slow Rayleigh fading assumption with the optimal (full feedback load) selective diversity scheduling scheme

Wireless scheduling algorithm can extract multiuser diversity (MUDiv) via prioritizing the users with best current channel condition. One drawback of MUDiv is the required feedback carrying the instantiations channel rate from all active users to the access point base station. This paper shows that this feedback load is, for the most part, unjustified. To alleviate this problem, we propose an optimal discrete rate switch-based multi-user diversity system (DSMUDiv) that allows reducing the feedback load while preserving the essential of the scheme performance. We examine DSMUDiv scheme using an absolute signal-to-noise ratio (SNR)-based scheduling mechanism, assuming all users are independent identical distributed (i.i.d.). We provide a theoretical analysis of the feedback load and the spectral efficiency for the DSMUDiv scheme and compare it with the optimal (full feedback load) selective diversity scheme. Slow Rayleigh fading is assumed. Our results show a reduction in the feedback load.

One of the most promising approaches to boost the communication efficiency in wireless systems is the use of multiuser diversity (MUDiv), where the fading of channels is exploited. The mechanism of scheduling the user with the best channel condition is called opportunistic scheduling (OS). In this paper, we propose a novel OS algorithm in wireless networks that reduces the feedback load with the aid of relaying. It is called relay-aided opportunistic scheduling (RAOS). We consider two schemes: non-greedy RAOS and greedy RAOS. In the non-greedy RAOS schemes, we consider two scenario: non-persistent and p-persistent, where the persisting occurs when no feedback is received via a relay. The RAOS algorithm requires users to feedback their signal-to-noise ratios (SNRs) either directly to the access point (AP) or via a relay. Furthermore, We analyse the RAOS algorithm under slow Rayleigh fading assumption and derive the closed-form expressions for the feedback load as well as the spectral efficiency. The result shows that the RAOS algorithm provides 55% feedback load reduction compared with other scheduling algorithms.

In this paper we analysis the performance of Infostation information transfer using a hybrid automatic repeat request (ARQ) technique combined with adaptive modulation (AM). The ARQ scheme works in selective-repeat (SR) mode combined with adaptive modulation and maximum ration combining (MRC). First, we explain how our hybrid ARQ/AM scheme works to transmit fragmented information files. Then, we present numerical evaluation of average number of channel access (ACHA) needed to complete a file transfer.