Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

Interference Calculation in Asynchronous Random Access Protocols using Diversity

The use of Aloha-based Random Access protocols is interesting when channel sensing is either not possible or not convenient and the traffic from terminals is unpredictable and sporadic. In this paper an analytic model for packet interference calculation in asynchronous Random Access protocols using diversity is presented. The aim is to provide a tool that avoids time-consuming simulations to evaluate packet loss and throughput in case decodability is still possible when a certain interference threshold is not exceeded. Moreover the same model represents the groundbase for further studies in which iterative Interference Cancellation is applied to received frames.Comment: This paper has been accepted for publication in the Springer's Telecommunication Systems journal. The final publication will be made available at Springer. Please refer to that version when citing this paper; Springer Telecommunication Systems, 201

The 30/20 GHz flight experiment system, phase 2. Volume 2: Experiment system description

A detailed technical description of the 30/20 GHz flight experiment system is presented. The overall communication system is described with performance analyses, communication operations, and experiment plans. Hardware descriptions of the payload are given with the tradeoff studies that led to the final design. The spacecraft bus which carries the payload is discussed and its interface with the launch vehicle system is described. Finally, the hardwares and the operations of the terrestrial segment are presented

Adaptive thresholding based optimal rate and MIMO mode selection scheme for IEEE 802.11n WLAN

The emergence of multiple antenna technology in IEEE 802.11n WLAN  has resulted in performance improvement in terms of throughput as well as transmission reliability as compared to legacy standards. Link adaptive transmission is critical to WLAN. Most of the existing algorithms for MIMO mode adaptation (between spatial multiplexing and diversity encoding) use fixed SNR switching thresholds for rate selection. The use of a fixed threshold in both MIMO modes, however, can only provide smaller throughput gain. The present studies on link adaptation do not consider the fundamental characteristic difference in the diversity encoding and spatial multiplexing encoding for MIMO. In this paper we propose a novel adaptive thresholding based optimal rate and MIMO mode (ORMM) algorithm for 802.11n wireless network. The proposed scheme adaptively switches between two SNR switching threshold vectors, separately determined for each MIMO mode analytically. Simulations over the Rayleigh fading channel shows that ORMM outperforms the existing approach of MIMO rate adaptation based on the use of fixed switching thresholds for rate selection

Exploiting the Path Propagation Time Differences in Multipath Transmission with FEC

We consider a transmission of a delay-sensitive data stream from a single source to a single destination. The reliability of this transmission may suffer from bursty packet losses - the predominant type of failures in today's Internet. An effective and well studied solution to this problem is to protect the data by a Forward Error Correction (FEC) code and send the FEC packets over multiple paths. In this paper we show that the performance of such a multipath FEC scheme can often be further improved. Our key observation is that the propagation times on the available paths often significantly differ, typically by 10-100ms. We propose to exploit these differences by appropriate packet scheduling that we call `Spread'. We evaluate our solution with a precise, analytical formulation and trace-driven simulations. Our studies show that Spread substantially outperforms the state-of-the-art solutions. It typically achieves two- to five-fold improvement (reduction) in the effective loss rate. Or conversely, keeping the same level of effective loss rate, Spread significantly decreases the observed delays and helps fighting the delay jitter.Comment: 12 page