Mohsen Sarraf

An OFDM all digital in-band-on-channel (IBOC) AM and FM radio solution using the PAC encoder

The advances in digital communications and compression algorithms have made more efficient and more robust transmission schemes possible. Radio broadcast systems have not fully utilized these advances to their benefit. All digital robust radio broadcast systems for the AM and the FM band are proposed. The proposed systems are based on orthogonal frequency division multiplexing (OFDM) technology in conjunction with PAC for both the AM and the FM bands. The Perceptual Audio Coder (PAC) developed by Bell Laboratories compresses audio signals very efficiently with CD-like quality at 96 kbps and stereo FM-like quality at 48 kbps. These are rates achievable with 200 kHz and 30 kHz bandwidths available per FM and AM station respectively. No new spectrum is required since the digital signals are transmitted within the current allocated FCC masks. In an FM channel, a wide-band data subchannel can be provided in addition to the 96 kbps error protected PAC audio information.

Frequency offset estimation in frequency selective fading channels

The challenge of frequency offset estimation in wireless channels and also the effect of delay spread on the performance of some of the existing algorithms is discussed. A new frequency estimation technique based on channel impulse response estimation which is desirable in wireless systems and has a fast convergence speed is addressed with some new practical implementation guidelines.

Performance analysis of Packet Loss Concealment in mobile environments with a two-state loss model

This paper presents and exercises a model to estimate the performance of Packet Loss Concealment (PLC) in wireless field environments. In particular, we estimate the probability of successfully receiving a random packet transmitted over an unreliable wireless link where a packet loss concealment algorithm such as the IETFs RFC 2198 standard schemes 1 and 2 are used. The model assumes a channel with a two-state loss system. Results generated are useful in understanding how packet loss concealment schemes can be designed to support high quality for real-time wireless applications such as VoIP on ad hoc networks.

A frequency offset estimation technique for nonstationary channels

In this paper a new parameter estimation technique based on channel impulse response estimation is introduced which is desirable in randomly time-varying systems such as burst transmission mobile systems since it is robust in environments with considerable delay spread, thus ideal for wireless channels, and has a fast convergence, thus desirable in burst transmission systems. The shortcomings of some of the existing algorithms are also discussed here.

Effect of slot size on TDMA performance in presence of per slot overhead

The problem of optimum slot size in the time division multiplexing (TDM) scheme in the presence of per slot overhead is addressed. Per slot overhead occurs in a variety of network structures. Messages are assumed to be of random length, so they may need to be segmented into several slots, and are assumed to be arriving according to a Poisson process. Optimum slot is derived as a function of input rate, message length distribution, overhead per slot, and number of stations. It is also shown how one will be penalized by deviating from this optimum slot size. Guidelines are provided on how to assign unequal slot sizes in cases where different stations have different traffic characteristics. It is shown that this is a cumbersome nonlinear optimization programming problem in general, which reduces to a Kuhn-Tucker optimization programming problem in light traffic situations.<<ETX>>

A frequency offset estimation technique for wireless channels

A new parameter estimation technique based on channel impulse response estimation is introduced which is desirable in wireless channels since it is robust in environments with considerable delay spread. It also has a fast convergence, and is thus desirable in burst transmission systems. The shortcomings of some of the existing algorithms are also discussed.

Performance analysis of the Outbound Call Management system

The Outbound Call Management (OCM) system automatically dials phone numbers from a long predetermined list for human agents. A technique is provided to determine the number of calls to launch for the Outbound Call Management system to achieve a good agent efficiency performance measure, giving the queuing tolerance level. Subsequently, an approximate method is introduced that calculates the efficiency of the system, and the number of trunks required, along with the probability that a called customer will join a queue due to lack of agents.<<ETX>>

Queueing time for the outbound call management system

The outbound call management (OCM) system was introduced by M. Sarraf (1989), and its performance was analyzed. In that work, although the probability of joining the queue by a random customer was given, the time spent in the queue was not addressed. The average time to empty a queue, once it is formed, is given, along with the average time the customer at the head of the queue has to wait before being served. The average time a customer spends in the queue lies between these two values. Some examples are given.<<ETX>>

Preassigned retransmission slots multiple access scheme (PARS)

A new multiple-access scheme for a finite number of stations, called preassigned retransmission slots (PARS), is introduced. The delay-throughput performance of the algorithm has been analyzed under single buffer assumption, and simulated under the infinite buffer assumption. Both performance studies show that the algorithm is stable and performs like slotted-ALOHA in light traffic situations and like time division multiple access (TDMA) in heavy traffic situations. The adaptation to traffic intensity is inherent in the algorithm and no dynamic control of any parameters of the algorithm is needed to achieve this property. Hence, implementation of PARS is much easier than some other algorithms with the same property. It is also shown that in cases in which traffic is not uniformly generated among stations, PARS performs better than TDMA, even in heavy traffic situations.<<ETX>>

A novel collision detection scheme for Wireless Sensor Networks using received signal dynamic range statistics

Wireless Sensor Networks (WSNs) have a limited power source which is a small battery installed in each node. The main concern in designing WSNs is how to extend the lifetime of network nodes. Power consumption in WSNs has been investigated in a lot of research. In this paper we propose a novel power saving algorithm which has a low computational complexity in comparison with existing coding/decoding schemes. Instead of decoding every received signal our proposed algorithm avoid the high computational complexity via analyzing the sanity of the received packet. So, the receiver can detect collisions and determine when the transmitted signals need to be decoded. Our proposed algorithm achieves a significant power saving due to avoid decoding of transmitted signals which involve in collisions. Based on two proposed algorithm metrics, thresholds, modulation schemes and different scenarios, we use MATALB to show performance gains of our proposed algorithm.