Wireless cellular networks are growing rapidly around the world. There is a huge demand in new improved wireless interactive multimedia services like video-on demand, multimedia conference and fast internet access. These services must be provided in a wide range of environments, spanning dense urban, suburban, and rural areas. Increased services, larger coverage area and lower costs have resulted in an increased air time usage and number of subscribers. Wireless operators find difficulty in handling billions of subscribers with variable traffic level and high mobility due to limited radio (spectral) resources. System capacity is a primary challenge for current wireless network designers.

Other challenges include,

i) The transmission through notorious wireless medium (presence of multipath, noise, interference and time-variations).

ii) The limited battery life of the user's hand-held terminal.

iii) Efficient radio resource management to offer high quality of service.

There is a need to investigate ways to improve the wireless system performance, increase the capacity & coverage of wireless communication and to fulfill the demand of increase in wireless communication services.

Design engineers are continuously looking for solutions that increase coverage and capacity in wireless system without the need for more cell sites or without using additional spectrum. Reevaluating antenna technology is one approach. Traditionally, system designs have employed omnidirectional and sectorized antenna technologies in cellular systems. But these approaches are limited in terms of capacity by uncontrolled interference. In last decades, Antenna arrays have emerged as a powerful technology in order to increase the link or system capacity in wireless systems. To achieve this, the gain and phase relationship between the elements of the antenna array must be known. Basically, the deployment of multiple antennas at either the transmitter or the receiver side of a wireless link allows the exploitation of two contrasting benefits: Diversity and Beam forming.

The multipath propagation is a well known phenomenon of wireless communication environments. The multipath causes amplitude and phase fluctuations and time delay in the signals received at the receiver. This effect is known as fading. It affects the receiver’s capability to detect the actual information from the noisy signal. However multi antenna systems take the advantage of multipath propagation by sending and receiving the same data signal by using multiple transmitting and receiving antennas via number of transmission paths. Each path is having independent fading statistics; hence the received signals are uncorrelated. The multiple received signals are used to find out the strongest signal, which can be further equalized and demodulated to get the desired signal with minimum error. This process is called as diversity. The process of reception/ combining the multiple signals can be either fixed or adaptive one. The fixed method gives the strongest signal at the receiver; however adaptive method exploits the directional properties of the channel. A receiver with multi-antenna elements can distinguish Multi Path signals with different Directions of Arrival (DOAs) and processes them separately. This allows the receiver to combine the different multipath signals in an intelligent way. In other words the signals are combined by adaptive algorithms and can automatically change the directionality of its radiation and/or reception pattern in response to the signal environment. Such systems are referred as Smart antennas. It is to be noted that Intelligence (smartness) is not in the antenna, but rather in signal processing (Combining) method. So antenna systems are smart. More specifically, generally co-located with a base station, a smart antenna system combines the outputs of multiple antenna elements with signal processing algorithms to transmit and/or receive RF signals in an adaptive, spatially sensitive manner. And for the transmit case, the signals at the antenna elements are created by the algorithm. The rapid growth in demand for smart antennas is fueled by two major reasons.

• First, the technology for high speed analog-to-digital converters (ADC) and
• Second, the tremendous improvements in high speed digital signal processing.

Even though the concept of smart antennas had been around since the late 50s, the technology required to make the necessary rapid and computationally intense calculations has only emerged recently. Early smart antennas, or adaptive arrays, were implemented in analog hardware. With the growth of ADC and digital signal processing (DSP); what was once performed in hardware can now be performed digitally and quickly. ADCs, resolutions that range from 8 to 24 bits, and sampling rates approaching 20 Giga samples per second (GSa/s), are now a reality. In time, superconducting data converters will be able to sample data at rates up to 100 GSa/s . This makes the direct digitization of most radio frequency (RF) signals possible in many wireless applications. At the very least, ADC can be applied to IF frequencies in higher RF frequency applications. This allows most of the signal processing to be defined in software near the front end of the receiver. In addition, DSP can be implemented with high speed parallel processing using field programmable gate arrays (FPGA). Smart antennas are the practical realization of adaptive array signal processing and have a wide range of interesting applications. These applications include, but are not limited to, the following:

Mobile wireless communications,

Software-defined radio

Wireless local area networks (WLAN),

Wireless local loops (WLL) ,

Mobile Internet,

Wireless metropolitan area networks (WMAN),

Satellite based personal communications services,

Radar,

Ubiquitous radar,

Many forms of remote sensing,

Mobile ad hoc networks (MANET),

High data rate communications,

Satellite communications,

Multiple-in-multiple-out (MIMO) systems, and

Waveform diversity systems.