Bit Error Rate Analysis in WiMAX Communication at Vehicular Speeds Using Nakagami-m Fading Model Biswojit Bose, Iftekhar Ahmad and Daryoush Habibi Centre for Communications Engineering Research, Edith Cowan University, Australia. Abstract—High speed wireless communication technologies such as Worldwide Interoperability for Microwave Access (WiMAX) have revolutionized the way of our day-to-day com- munication and opened opportunities for many innovative ap- plications. The 802.6m version of WiMAX offers data rates up to 1 Gbps for fixed communications and supports mobility up to 350 km/h. While WiMAX technology’s capacity to deliver high data rates in a fixed environment is beyond any doubt, the standard is not fully optimized yet for mobile communication at high vehicular speeds. At high vehicular speeds, rapid changes in surrounding environments, cause severe fading at the receiver, resulting a drastic fall in throughput and unless any proactive measure is taken to combat this problem, throughput becomes insufficient to support many applications, particularly those with multimedia contents. Bit Error Rate (BER) estimation is an integral part of any proactive measure and recent studies suggest that Nakagami-m model performs better for modeling channel fading in wireless communications at high vehicular speeds. No work has been reported in literature that estimates BER at high vehicular speeds in WiMAX communication using Nakagami-m model. In this paper, we develop and present an analytical model to estimate BER in WiMAX at vehicular speeds using Nakagami- m fading model. The proposed model is adaptive and can be used with resource management schemes designed for fixed, nomadic, and mobile WiMAX communications. Index Terms—WiMAX, vehicular speeds, bit error rate, Nakagami-m. I. I NTRODUCTION W IMAX is a popular next generation wireless tech- nology that currently serves more than 620 million people in approximately 147 countries. WiMAX is popular for its capacity to deliver high throughput at a fixed communica- tion environment. In a mobile communication environment at high vehicular speeds, this throughput decreases sharply, often providing a connection only service with no guaranteed data rate. The 802.16m version of WiMAX standard acknowledges this problem and indicates that the 802.16m is fully optimized for stationary and pedestrian speeds (0-10km/h) [1]. At speeds between 10-120km/h, WiMAX users experience a gradual degradation of service and at speeds above 120 km/h, only a connection can be maintained without any assurance on data rate. WiMAX standard incorporates Orthogonal Frequency Di- vision Multiplexing (OFDM) and Orthogonal Frequency Di- vision Multiple Access (OFDMA) [2] for achieving better spectral efficiency and data rates. The OFDM is a robust technique that overcomes the frequency selectivity problem Figure 1. Multipath fading problem in wireless communication at vehicular speeds. of the channel and provides higher throughput. In OFDM systems, total bandwidth is divided into multiple sub-carriers using Fast Fourier Transformation (FFT) operation where the sub-carriers are orthogonal to each other. Sub-carriers are divided into data, pilot, DC and guard sub-carrier. The data, pilot and guard sub-carriers are used for transmitting data, pilot symbols and guard information for limiting interference, re- spectively. The OFDMA technique is based on OFDM, which provides multiuser access to a channel by dividing the sub- carriers into subsets of sub-carriers. For supporting mobility, mobile WiMAX extends its physical layers and incorporates the scalable OFDMA (S-OFDMA) technique. By adopting scalable PHY architecture, it can support a wide range of bandwidths. The scalability is implemented by varying the FFT from 128 and multiple of 128. Table-1 summarizes the primitives used for mobile WiMAX PHY. At high speeds, doppler shift causes inter-carrier interference (ICI) and due to small sub-carrier spacing, ICI possibilities on larger FFT is higher than lower FFT. WiMAX forum therefore recommends smaller FFT and simpler modulation at high vehicular speeds. In a high mobility scenario, relative motion between trans- mitters and receivers results in rapid time variation and high doppler shift. Accumulating dynamically changed multipath effects and noise, a significant fluctuation in received signal strength is observed in the channel. Fading like this is often modelled in literature with Rayleigh fading model. Rayleigh fading model has not been challenged until very recently when researchers started to focus on the throughput problem at vehicular speeds. Rayleigh model works on the assumption that the resultant fading arises from a large number of uncorre- lated partial waves with identically distributed amplitudes and uniformly [0, 2π] distributed random phases. This assumption is highly optimistic in a mobile communication environment at high vehicular speeds and the more realistic assumption 978-1-4673-1881-5/12/$31.00 ©2012 IEEE