Guillermo E. Atkin

An efficient modulation/coding scheme for MFSK systems on bandwidth constrained channels

The performance of a bandwidth-efficient multiple-tone modulation scheme for M-ary frequency-shift keying (MFSK) is presented. The use of balanced incomplete block (BIB) designs is proposed to form the signaling frames. On each symbol interval the modulator selects a group of elements from a BIB design and divides its energy into the orthogonal waveforms corresponding to these elements. The multiple-tone FSK scheme based on these block designs is shown to increase greatly the bandwidth efficiency of a conventional M-ary FSK system. An implicit diversity is incorporated in the modulation scheme. Thus, a performance improvement comparable to that obtained by using time or frequency diversity is shown on a Rayleigh fading channel and also on an interference channel with partial-band Gaussian noise. The multiple-tone scheme based on this design is compared to a multiple-tone scheme based on Hadamard matrices suggested by J.F. Pieper et al. (1978). It is shown that similar performance is achieved on a fading channel, while an advantage close to 4 dB is obtained for the proposed scheme on an AWGN (additive white Gaussian noise) channel. >

Framework for delivering IPTV services over WiMAX wireless networks

The Internet Protocol Television (IPTV) service is becoming more and more popular among telecommunications companies because it can deliver TV programs anytime anywhere. Based on IP protocol, IPTV features advantages like bandwidth efficiency and ease of management. IPTV supports both broadcast and unicast services like LiveTV and VideoOnDemand. WiMAX wireless system, capable of ensuring high bandwidths and low latencies, is suitable for delivering multimedia services. In addition, it also provides wide area coverage, mobility support, and non-line-of-sight operation. Therefore, WiMAX is a promising solution for delivering IPTV services anytime anywhere, especially to rural areas or remote locations. This paper identifies the challenges in delivering IPTV over WiMAX wireless system and proposes a framework to provide some solutions to those challenges, at MAC and Physical layers. Taking advantage of the WiMAX features, IPTV services can be delivered at low costs and with high audio/video service quality.

Coded multipulse modulation in optical communication systems

An optical communication system using coded multipulse position modulation is described. The position of the pulses in each signalling interval are derived from general binary constant weight codes. The combined coding and modulation of multiple pulses provides a minimum distance between any two signaling frames. Photon counting is used at the receiving end for noiseless optical channel in which only quantum noise exists. For noisy optical channel with avalanche photodetector, threshold demodulation is used in which an optical pulse is considered present in a slot where the photoelectron count exceeds a given threshold. It is shown that this multipulse system gives better performance than the conventional single pulse system. The performance analysis can be applied to and binary constant weight code since only the general parameters of length, minimum distance, and weight of the code are needed. >

Cancellation of nonlinearities in bandpass QAM systems

An orthogonalized input-output characterization of nonlinear bandpass quadrature amplitude modulation systems with memory is developed. The orthogonal expansion is used with a nonlinear canceller structure to counteract the effect of nonlinear distortion introduced by high-power amplifiers at the transmitter. It is shown through simulations that when the transmitted symbols are known at the canceller, relatively simple structures can eliminate the effect of the nonlinearity. Even when the transmitted symbols are not known at the canceller, the improvement in performance with the nonlinear canceller, with respect to a linear receiver, is significant. >

On the performance of a hybrid frequency and phase shift keying modulation technique

The performance of a hybrid modulation technique derived from binary frequency shift keying is presented. In the hybrid scheme, each frequency is allowed to be phase modulated with any of p discrete, equally spaced phase shifts. The spectral separation between frequencies is chosen to make the carriers orthogonal, thus generating a multidimensional modulation scheme. The performance of complete and expurgated phase codes is examined for the Gaussian and Rayleigh fading channels, and their spectral characteristics are determined. >

Orthogonal convolutional coding for the PPM optical channel

Several coding alternatives have been analyzed to improve the performance of the ideal optical pulse position modulation (PPM) optical channel, although it has been shown that performance improvements are difficult to obtain for transmission efficiencies over 1 nat/photon. In the present work, an orthogonal convolutional coding scheme is proposed, achieving better performances than previous coding alternative, over a wide range of efficiencies. Furthermore, a concatenated coding scheme using an orthogonal convolution code as an inner code and a Reed-Solomon code as an outer code is proved to be effective, achieving operation points over 3 nat/photon, with performances that cannot be obtained with other coding schemes. >

Performance of optimum wavelet waveform for DS-CDMA chip waveform over QS-AWGN channel

In this paper, we search for a better chip waveform based on orthogonal wavelets for direct sequence-code division multiple access (DS-CDMA) signals to improve the probability of error (Pe) performance with minimal signal bandwidth variations. First, we derive the Pe expression over a quasi-synchronous additive white Gaussian noise channel for DS-CDMA signals, which use various pulse shaping waveforms including orthogonal wavelets as chip waveforms. It is observed that this expression depends on the chip waveform. Then, we design an optimum wavelet by using the relationship between wavelets and filter coefficients to reduce the probability of error. The DS-CDMA system using the optimum wavelet waveform results in a lower probability of error than those using the conventional chip waveforms such as raised cosine, half-sine and rectangular waveforms. Especially, the Pe of the optimum wavelet-based scheme becomes significantly better than those of the conventional chip waveforms-based schemes under the heavy loading that is the case for commercial wireless systems. When the systems work with full load (i.e. the number of users equals the processing gain), the optimum wavelet-based system results in 0.5, 2.1 and 4 dB better SNR values than those of the raised cosine, half-sine and rectangular-based systems, respectively, for a Pe value of 10−3. Copyright

Steiner system signal sets over the Gaussian channel

Steiner systems constitute an example of codes that achieve asymptotic error-free transmission for the Gaussian channel. In contrast to simplex and orthogonal codes which also have this property, these codes make more efficient use of the bandwidth by reducing the required dimensionality to generate the M signals. Tight upper bounds for the symbol error probability are derived for coherent and noncoherent detection that include previously reported results as special cases. The relative bandwidth efficiency with respect to orthogonal codes is presented, and a combined performance plot is given that allows a meaningful comparison between the different coding schemes considered. >

Scale-time-code-division multiple access (STCDMA)

In this work, a wavelet-based multiple access system, STCDMA (scale-time-code-division multiple access), which is based on the scale, time, and code orthogonality has been described and its performance has been analyzed for synchronous transmission in an AWGN channel. In a synchronous AWGN channel, Hadamard codebased PN sequences keep their orthogonality and hence STCDMA achieves optimum single-user BPSK performance by using a conventional single-user detector for each user. It also supports a larger number of users than conventional DS-CDMA (six or seven times more than DS-CDMA) if the first (coarsest) scale is thought to be traditional DS-CDMA. When we use other wavelets than the Haar wavelet, or the signature waveforms exhibit some correlation in other environments such as asynchronous AWGN channel and the multipath propagation medium, the system will have multiple access interference.

Symbol error rate analysis for cooperative diversity networks by distributed embedded space time code

In this paper a special version of cooperative distributed space time coding for the relays network is proposed. According to this system model relays cooperatively collaborate with the sources to transmit the space time code to the destination. Process of the transmission consists of two phases. In the first time phase source broadcast the information to the destination and relay. In the next time phase, the source and relay cooperatively send signals to the destination by using an embedded space time coding. Structure of embedded space time code is based on singular value decomposition of circulant matrix. Relays are assumed to be non-regenerative amplify-and-forward. Theoretical analysis for calculating the bit error rate (BER) has been done based on maximum ratio combining (MRC). Simulation results for the case of one relay, one source and destination through the Rayleigh fading channel has been done and compared with the scenario when transmitter and relay used the Alamouti code.