Salim Kahveci

Performance analysis of zigzag-coded modulation scheme for WiMAX systems

Abstract WiMAX is an OFDM-based technology that supports point-to-multi-point broadband wireless access for next-generation radio access such as 4G. In this paper, we evaluate bit-error-rate performance of fixed WiMAX (IEEE 802.16d) and mobile WiMAX (IEEE 802.16e) transmission systems with various modulations and channel coding techniques. In the digital communication phenomenon, coding schemes are broadly used as a term mostly referring to the forward error correction code. The advantage of the forward error correction code is that retransmission of data can often be avoided. The simulation results include performance analysis based on bit-error-rate versus signal-to-noise-ratio plots and spectral efficiency of different modulation and coding schemes according to the IEEE 802.16 general standard. The results show that the proposed zigzag-coded modulation possesses a stronger error correcting capability according to the Reed Solomon with Convolutional code for both fixed WiMAX and mobile WiMAX standards.

A channel detection technique based on Max-Log-MAP algorithm for wireless indoor system

This study introduces a new low complexity Max-Log-MAP based channel estimation technique operating in a multi-path band limited channel. The proposed estimation technique is based on an iterative procedure derived through the maximum a posteriori probability approach. Wireless communication channels often undergo frequency selective fading that leads to inter-symbol interference, which limits the performance of wireless indoor systems. Performance of the algorithms is assessed by combined analysis and simulation. Results are presented and compared against the performance of conventional Log-MAP algorithm. The obtained results show that the required bit-error-rate performance can be achieved with a lower number of iterations using the proposed low complexity algorithm compared to using the conventional Log-MAP algorithm.

LMS and RLS equalizer performances of ultra wideband system in body area network channel

This paper provides baseband simulation performed ultra wideband (UWB) system with direct sequence spread spectrum (DSSS) presented in the IEEE 802.15.6 wireless body area network (WBAN) standard. Body area network channel is used as a wireless communication channel. Against the multi-path effects caused by this channel, least mean squares (LMS) and recursive least squares (RLS) equalizers are used in the UWB receiver. Signal to noise ratio (SNR) - bit error rate (BER) performances are given due to usage of equalizations and the DSSS. Finally, 10-3 - 10-5 bit error rates are obtained in 6 - 9 dB SNR levels in the simulations realized in baseband with DSSS.

Dynamic Look-Up-Table-Based Maximum a Posterior Probability Algorithm

In this paper, a Look-Up-Table (LUT) based calculation for implementing log-likelihood ratio (LLR) of the Maximum a Posterior (MAP) decoder is introduced and analysed. In the region of low signal to noise ratio, the analysed performances of turbo coding have been found very satisfying. However, when implementing the MAP turbo decoder, the required calculation for LLR is too complex prohibiting its applications. In order to reduce the complexity a dynamic-LUT based simplification is proposed whereas a static-LUT never converge the expectations, since the limited size and resolution of LUT dramatically degrade the performance. In order to maintain simplicity for a high performance implementation, a dynamic LUT, which has partial resolutions in separate decision regions and being re-calculated for further iterations of decoding, is proposed. One of the most important results obtained is that our proposed dynamic-LUT based MAP algorithm removes “ln(·)” process, which is the natural logarithm in LLR’s calculation. Therefore, it reduces high computational complexity in the MAP algorithm with some reasonable performance degradations.

Evaluation of energy efficiency of fifth generation mobile systems

There has been active research worldwide to develop the next generation, i.e., fifth generation, wireless network. Next generation mobile communication networks are broadening their spectrum to higher frequency bands (above 6 GHz) to support a high data rate up to multigigabits per second. This work examines how to substantially improve energy efficiency for next fifth generation mobile communication systems. It is depicted how by limited exchange of information between neighboring base stations it is possible to maintain quality of service, over a range of traffic loads, while enabling inactive base stations to sleep. Performance of distributed energy efficient topology management schemes are compared against the system without topology management. Performance evaluation is examined using both analytical and simulation based models. Extensive numerical results show that the schemes deliver a significant energy reduction in energy consumption in the mobile network systems.

Wireless measurement of thermocouple with microcontroller

High sensitive measurement is needed for high and low temperature determination in the scientific and industrial applications. In this study, measurement and calibration system design of K-type thermocouple used in the temperature measurements was examined. The system was performed in two ways using thermocouple integrated circuit and analog-digital converter. Temperature sensors were used for thermocouple cold junction measurement. By adding a wireless transceiver, wired and wireless usages were developed. Control, calibration and display processes were performed with the written interface program. The program was written in a way that practically the thermocouple can be calibrated with reference temperatures. Sample measurements of the established system were compared with the mercury thermometer according to the calibration types. The calibrated results of the performed system with analog-digital converter were found to be the closest to reference thermometer.

Performance of parallel concatenated zigzag codes for different segment length

General turbo codes have an excellent bit-error-rate (BER) performance at low signal-to-noise ratios (SNR) in additive white Gaussian noise (AWGN) channels. However, the standard turbo decoding algorithm is highly complex. To reduce its decoding computational complexity, zigzag codes are currently used. A zigzag code is a family of error-correcting codes similar to the single parity check codes. It is an important issue, how the segment length called J and the interleaver can affect concatenated zigzag code performance. In this study, the segment size and interleaver structure are investigated in order to obtain a high bit-error-rate performance for the concatenated zigzag code with four encoders and three random interleavers. Realized computer simulation results are compared with/without interleaver for various values of J over a noisy channel.

Some cooperative relaying techniques for wireless communication systems

A cooperative wireless communication system is generally consists of a source node, a destination node, and a one or more relay(s) nodes. Relay nodes can be useful to enhance the robustness of the desired transmission to channel fading and interference. For a single relay system, the simplest relaying techniques are the amplify-and-forward (AF) and decode-and-forward (DF). In the study, we will explain the single relay systems and analyze the performance of those structures.

Adaptive rate Zigzag coding in interference channels

In practice, channels in wireless communication systems are time-variable. Because of the variability of the channels in wireless systems and networks, the performance of error-control coding can be improved by adapting the rate of the code to the channel conditions. Thus, the bit-error performance of error-control coding system can be improved. In this study, an adaptive rate error control coding with concatenated Zigzag coding is investigated. The bit-error-rate performance of the adaptive rate Zigzag coding system is evaluated for channels with interference and noise.

Wireless cooperative communication with simple coding

Wireless communications performance is badly affected by channel fading issue. Some diversity techniques are used to reduce the impact of fading by conveying data over multiple independent fading channel paths and combine them at the receiver side. Cooperative diversity is a novel communication technique where multiple terminals use their resources in cooperative manner to form a virtual array that realizes spatial diversity gain in a distributed fashion. Cooperative relay system can obtain reliable communications, capacity gain and energy saving by mutual relaying among users of wireless network.