Opportunistic scheduling provides a good chance to improve wireless system performance by exploiting the underlying channel condition. There has been a lot of work on opportunistic scheduling, but the problem of finding the right feedback mechanism to convey channel information has largely been untouched. In emerging multichannel systems, the per- channel feedback induces a substantial amount of feedback overhead and requires high computational complexity. To reduce the feedback overhead, we consider an opportunistic feedback strategy that activates the channel feedback opportunistically according to the channel condition. Then, we combine the opportunistic feedback with the best-n channel feedback scheme where a mobile user chooses the best n channels and transfers this information to the base station. We analyze the throughput and the amount of channel feedback information for proportionally fair opportunistic scheduling under Rayleigh fading i.i.d. channels. The numerical results confirm that our partial feedback schemes achieve a remarkable reduction in the amount of feedback information at the cost of slight throughput degradation, thereby saving the scarce wireless uplink bandwidth and limited battery power.

Partial Channel Feedback Schemes Maximizing Overall Efficiency in Wireless Networks

In this paper, a packet pre-classification media access control protocol based on a carrier sense multiple access with idle detection (CSMA-ID) scheme is investigated for supporting IP packets over all-optical WDM ring networks. The purpose of the protocol is to increase throughput and to decrease the packet transmission delay of IP packets over optical networks in a metropolitan area network. This protocol avoids both packet collision and packet fragmentation. In order to improve the utilization of the network, the packets transmitted from a local area network are first pre-classified into various class queues of an access point (AP) according to their length. After checking the available space based on the wavelength received by the receivers of the AP, the packets in the queues are transmitted. An analytical model is developed to evaluate the performance of the protocol, with simulation results showing good network efficiency. The proposed network has short-term variations that introduce unfairness conditions. This problem could be overcome by assigning a quota on individual queues to allow all queues fair access. Copyright © 2008 John Wiley & Sons, Ltd.

Performance evaluation of CSMA-ID MAC protocol for IP over WDM ring networks

This paper presents the developed orthogonal frequency division multiplexing (OFDM) baseband processor employing adaptive modulations to grouped subcarriers, and its demonstration in millimeter-wave wireless indoor links. Channel measurements and characterizations are performed in line-of-sight (LOS) office environments where the developed OFDM system is supposed to be used. The OFDM baseband processor utilizes 192 data subcarriers among 256 FFT numbers. To minimize bit-error-rate (BER) performance in frequency selective channels of millimeter-wave wireless indoor links, these 192 data subcarriers are grouped into 24 subcarrier groups and independently modulated according to channel characteristics in each subcarrier group. We demonstrate it incorporating with the developed 70 GHz self-heterodyne transceiver. BER measurements and maximum TCP throughput test are performed in practical millimeterwave indoor environments. The results verify the advantages of the proposed adaptive modulation in OFDM and show better BER performance as well as higher throughput performance than a typical OFDM system.

Implementation of an OFDM baseband with adaptive modulations to grouped subcarriers for millimeter-wave wireless indoor networks

Opportunistic scheduling can significantly improve wireless network performance by exploiting the feedback information that conveys the underlying channel condition. In emerging multichannel systems, the perchannel feedback induces a substantial amount of feedback overhead and requires high computational complexity. To reduce the feedback overhead, we consider an opportunistic feedback strategy that activates the channel feedback opportunistically according to the channel condition. Then, we combine the opportunistic feedback with the best-n channel feedback scheme where a mobile user chooses the best n channels and transfers this information to the base station. We analyze the throughput and the amount of channel feedback information for proportionally fair opportunistic scheduling under Rayleigh fading i.i.d. channels. The numerical results confirm that our partial feedback schemes achieve a remarkable reduction in the amount of feedback information without a significant throughput degradation, thereby saving the scarce wireless bandwidth and limited battery power.

Selective channel feedback mechanisms for wireless multichannel scheduling

Emerging systems like OFDMA and MIMO systems require multichannel scheduling over a wireless link. In this paper, we focus on the case that the number of channels to be assigned to a mobile terminal is limited, which we call limited matching. This case often occurs over a MIMO downlink when the number of receive antennas at a mobile user is smaller than that of transmit antennas at the base station. When the system exploits channel-aware opportunistic scheduling based on the channel feedback, finding the sum of channel gains by the limited matching is an NP-complete problem. To solve it easily, we can use the Hungarian algorithm, but its complexity is still too high and not amenable to performance analysis. Hence, we develop a heuristic algorithm, and analyze its cell throughput. Also, we investigate its performance when the channel feedback information is partially available. For analytic simplicity, we consider proportionally fair (PF) scheduling that is widely accepted as an opportunistic scheduler. Numerical results demonstrate that our heuristic limited-matching scheduling algorithm works well with partial channel feedback.

Multichannel wireless scheduling under limited terminal capability

In this paper, we investigate the performance of adaptive loading orthogonal frequency-division multiplexing (OFDM) under Rayleigh fading with maximal ratio-combining (MRC) diversity at the receiver. We assume that channel-state information is available at both the transmitter and the receiver. Closed-form expressions for the lower bound on the average capacity of OFDM transmission under Rayleigh fading are provided for ideal MRC diversity. Simple approximate expressions for the average capacity of the Rayleigh-fading channel are also provided for the high signal-to-noise ratio (SNR) case. In the second part of this paper, a maximum-rate adaptive-loading strategy is derived for uncoded quadrature-amplitude-modulation modulated OFDM. Simple lower bound expressions and high-SNR approximations are provided for the average spectral efficiency of the maximum-rate adaptive-loaded uncoded OFDM under Rayleigh-fading channel conditions. According to the results, the performance of the uncoded adaptive-loading OFDM is about 8.5 dB inferior to the capacity bound at 10/sup -5/ symbol error probability under frequency-selective Rayleigh fading.

Performance analysis of adaptive loading OFDM under Rayleigh fading

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Performance analysis of adaptive loading OFDM under Rayleigh fading