Bit Loading and Peak Average Power Reduction Techniques for Adaptive Orthogonal Frequency Division Multiplexing Systems

In a frequency-selective channel a large number of resolvable multipaths are present which lead to the fading of the signal. Orthogonal frequency division multiplexing (OFDM) is well-known to be effective against multipath distortion. It is a multicarrier communication scheme, in which the bandwidth of the channel is divided into subcarriers and data symbols are modulated and transmitted on each subcarrier simultaneously. By inserting guard time that is longer than the delay spread of the channel, an OFDM system is able to mitigate intersymbol interference (ISI). Significant improvement in performance is achieved by adaptively loading the bits on the subcarriers based on the channel state information from the receiver. Imperfect channel state information (CSI) arises from noise at the receiver and also due to the time delay in providing the information to the transmitter for the next data transmission. This thesis presents an investigation into the different adaptive techniques for loading the data bits on the subcarriers. The choice of the loading technique is application specific. The spectral efficiency and the bit error rate (BER) performance of adaptive OFDM as well as the implementation complexity of the different loading algorithms is studied by varying any one of the parameters, data rate or BER or total transmit power subject to the constraints on the other two. A novel bit loading algorithm based on comparing the SNR with the threshold in order to minimize the BER is proposed and its performance for different data rates is plotted. Finally, this thesis presents a method for reducing the large peak to average power ratio (PAPR) problem with OFDM which arises when the sinusoidal signals of the subcarriers add constructively. The clipping and the probabilistic approaches were studied. The probabilistic technique shows comparatively better BER performance as well as reduced PAPR ratio but is more complex to implement

The Bit Error Rate (BER) Performance in Multi-Carrier (OFDM) and Single-Carrier

The spectacular growth of wireless communication tools has escalated the number of mobile subscribers from almost 700 million in 2000 to more than 4 billion in 2009. The huge number of subscribers has led to several issues with how service is provided. The high user demand has forced developers to overcome the problems of the old analog systems and to introduce OFDM as a promising technique that can fulfill users\u27 high demands. This technique matches well with high data rate connection and provides a higher capacity for the subscribers\u27 usage. The OFDM, as a multi-carrier, is more complex than the single-carrier transmission scheme. However, the OFDM technique maintains better performance for high data rate in terms of bit error rate (BER). In this thesis a comparison has been presented between the multi-carrier OFDM and the single-carrier to prove, in a simulation form, the theoretical point of view. Despite the advantages of using the OFDM scheme, there are several drawbacks. One of these negatives is the high peak to average power ratio (PAPR). To overcome this problem, there are power reduction techniques that can be applied to the signal to reduce the high power. One of these techniques is the clipping and filtering technique. A maximum level is sited for the transmitted signal to reduce the power and afterward, the signal goes through a filter to remove the influence of the in-band distortion and out-of-band radiation

An efficient reconfigurable peak cancellation model for peak to average power ratio reduction in orthogonal frequency division multiplexing communication system

The peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) communication system will be reduced using reconfigurable peak cancellation (RPC). RPC will also aid in improves the error vector magnitude (EVM) and reduces adjacent channel leakage ratio (ACLR) in OFDM communication system. The proposed RPC design methodology and practical implementation using field programmable gate array (FPGA) are discussed. The proposed RPC has been demonstrated using VIRTEX-7 XC7Z100 dual-core FPGA device with less hardware difficulty and minimum utilization of FPGA resources. The proposed RPC improves the efficiency of OFDM communication process by reducing complementary cumulative distribution function (CCDF) with respect to instantaneous power in dB. A comparison analysis was done between the existing selective mapping (SLM) method with proposed RPS method with respect FPGA resource utilization. The proposed RPC is implemented using VIRTEX-7 XC7Z100 dual-core FPGA device. Its effectively utilizing sub-carriers, fast Fourier transform (FFT) filter, bandwidth, and sampling frequency. Due to parallel switching operation, it reduces the PAPR, ACLR and improves EVM in OFDM signal with less hardware complexity

Analysis of PAPR in OFDM with CSS

The present trends in wireless communication industry are in light of multi-carrier transmission technique for example, Orthogonal Frequency Division Multiplexing (OFDM) which is very encouraging as far as higher data rates and better resistance to frequency selective fading. Wireless communication standards like IEEE 802.11a/g/n/ac, IEEE 802.16e and numerous others utilize one or other variety of OFDM, for example, OFDMA and MIMO-OFDM. However, the immense drawback of the OFDM system is its high Peak to Average Power Ratio (PAPR). Every one of these utilizing the linear power amplier at the transmitter side so its operating point will go to the saturation point because of the high PAPR which prompts in-band distortion and out-of-band radiation. This problem can be avoided by increasing the dynamic range of the power of amplifier that leads to high consumption of power and cost at the base station. To battle the impact of high PAPR, a few PAPR reduction techniques have been contrived throughout the most recent couple of decades. Every one of these techniques need to strike a trade-off among a few parameters, for example, computational complexity, PAPR reduction performance, BER performance and others. Depending upon the requirement, the most proper technique is thus chosen. PTS system has been in presence since 1997 and gives an exceptionally successful PAPR reduction procedure with no restriction on the most extreme number of subcarriers. However the technique experiences an intense issue of high computational complexity. In this course a novel methodology which offers same PAPR diminishment and significantly reduces the complexity of the system by preserving the basic principle of the standard PTS technique is designed. The various quantities of IFFT blocks has been replaced by a single block to decrease the complexity of the framework. The proposed technique has been simulated and the PAPR reduction performance of the new technique has been compared with that of original PTS technique. Similarly, the complexities of the two techniques are compared based on the block diagrams. The proposed technique is applied to the multiple antenna system to reduce its PAPR. This system can increase the diversity to combat the deep fades that occurred due to frequency selective fading. This multiple antenna system has been simulated and the PAPR reduction of each antenna is analysed and compared with the standard PTS technique