System Performance Improvement For Ofdm System Over Generalized K Fading Channel

The market for wireless communications has experienced incredible growth over recent years and wireless LANs have rapidly become a very

There are four major techniques that allocate capacity for wireless WAN communications. These techniques are Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), and Orthogonal Frequency Division Multiplexing (OFDM). (Goleniewski, L. 2007) Each technique has pros and cons when compared amongst each other. The following is a summary of why each technique has a need, and some of the challenges that come with that technique.

Multicarrier modulation provides immunity to fading caused by data transmission over mul-tipath fading channels or frequency- selective fading channels. Each of the subchannel expe-riences flat fading due to the decreased bandwidth. Also, due to the increase in the symbol period, it provides enhanced immunity to ISI. Another advantage of multicarrier modulation technique is it can provide better spectral efficiency compared to single carrier modulation, since the spectrum of the subcarrier can be overlapped.

During the past decade, OFDM has been adopted in many wireless communication standards networks, including European digital audio broadcasting system, and terrestrial digital video broadcasting, and satellite terrestrial interactive multiservice infrastructure in China. In addition, OFDM has been considered or approved by many groups are working in IEEE standard, such as IEEE 802.11a/g/n standard network, IEEE 802.15.3a, and IEEE 802.16d/e.

In this paper, we have considered SC-FDMA for both the links, taking the UE limitations into considerations. The advantages and challenges of using SC-FDMA for downlink are well analyzed in [18].

The wireless channel is different and much more unpredictable than the wire line channel because of factors such as multipath and shadow fading, Doppler shift, and time dispersion or delay spread. These factors are all related to variability introduced by mobility of the user and the wide range of environmental conditions that are encountered as a result.

Repeaters for digital TV broadcasting can use either analogue or digital techniques. The purpose of using repeater is to boost signals into areas of weak coverage in any radio communication system. However wave interference means the repeater usually requires a frequency shift for analogue modulated signal. For digitally modulated signal it may be possible to use same frequency.

Orthogonal Frequency Division Multiplexing or OFDM is a modulation format that is being used for many of the latest wireless and telecommunications standards.

As multimedia services gain momentum, new broadband access technologies emerge to address the specific requirements of such services. To this purpose, there exist several traditional first mile solutions, leveraging cables or fibers, and a novel family of Broad¬band Wireless Access (BWA) technologies. Among BWA tech¬nologies, the IEEE 802.16 standard [1] is considered the leading technology for the provision of Internet-based broadband services in wide

During the last decade, MIMO techniques in wireless industry have gained a huge interest in the study. MIMO is treated as an extension of conventional smart antenna systems (SAS). In SAS, techniques of beamforming are deployed and the optimal antenna weighting vector that determines antenna radiation pattern is computed based on the optimal criterion such as maximum signal-to-interference plus noise ratio (SINR), minimum mean square error (MMSE) [8]. The ability to exploit and use the multipath propagation can be considered as one of the major advantages of MIMO systems. In contrast to transmit beamforming schemes, channel state information (CSI) is generally not required at the transmitter of MIMO systems. MIMO techniques for transmitting systems can be majorly divided into two categories: spatial multiplexing and space-time coding (spatial diversity techniques). In spatial multiplexing technique, it increases the data rate (throughput) over a MIMO dedicated

OFDM provides the frequency selective channel which can able to divides the frequency band into multiple sub channels and each sub channel carries a different stream of symbols. There is flat frequency response throughput each sub channel when there is narrow bandwidth of each sub channel. Therefore OFDM able to transform a frequency selective channel into set of multiple flat-fading channels. Simultaneously when M transmit antennas used an OFDM transmitter, and N receive antenna used OFDM front end then L flat fading MIMO channel is formed from MIMO frequency selective channel with having dimensions equals to MxN. Earlier traditional space time codes were not optimal for takeout the additional

Transmit diversity: In this multiple antenna are used to transmit same block of code. the code is divided into 2 or 4 blocks. The numbers 2 or 4 are critical.lte does not support transmit diversity greater than 4.

WiMax (worldwide Interoperability for Microwave Access) is the recently approved IEEE 802.16 wireless metropolitan area network (MAN) standard for wireless access. WiMax is the real wireless architecture by which the wireless access range can extended to 49.6Kms compared with Wi-Fi 91mts and Bluetooth’s 9mts. WiMax 802.16

Where and are the average values of signal strength depending on whether the bit corresponds to 1 or 0 in the bit stream [9]. The relationship between Q-factor and bit error rate is given as:-

The High Frequency (HF) radio band is defined as the range of frequencies in the radio spectrum between 3 and 30 megahertz . Military organizations have used HF radios for both strategic and tactical communications for more than 80 years. However with the development of satellite communications (SatCom) use of HF communication were de-emphasized and fell in to disuse. In contrast to this importance of HF communication still existing for military applications. The militaries around the world must have a robust long range communication system that does not rely on existing communication infrastructure in emergencies, since the satellite comms and other comms infrastructure will present most lucrative targets for the enemy.