Performance Analysis of Extended Channel

Long Term Evolution (LTE) is the latest standard proposed by the 3GPP towards 4G. This paper uses an accurate perform analysis of complete uplink LTE study. Multiple input multiple output (MIMO) techniques have gathered much attention in recent years as a way to improve drastically the performance of wireless mobile communications. Simulated Results compare different channel estimation techniques showing significant difference among them, such as Extended Pedestrian A, Extended Vehicular A, Extended typical urban , High Speed Train Condition(HSTC) are considered and the measurement data is compared for the Localized and Distributed SC-FDMA mapping methods. From the results, we find that Localized SC-FDMA outperforms Distributed SC-FDMA in terms of SNR and BER . Keywords— SC-FDMA, MIMO, Extended Pedestrian A, Extended Vehicular A, typical urban, Doppler Shift. 1.INTRODUCTION The ever growing demand for multimedia services, high mobility, and global connectivity has resulted in recent years in an exploration of new technologies for wireless communication systems. Single Carrier Frequency Division Multiple Access (SCFDMA) is a promising technique for high data rate uplink communication and has been adopted by 3GPP for it next generation cellular system, called Long-Term Evolution (LTE) [2]-[3]. SC-FDMA is a modified form of OFDM with similar throughput performance and complexity. In 3GPP Long Term Evolution (LTE), SCFDMA has been assumed for uplink transmission, whereas the Orthogonal Frequency Division Multiple Access (OFDMA) signalling format has been exploited for the downlink transmission. Thus SC-FDMA takes over all the advantages of OFDM over other well-known techniques such as TDMA and CDMA. Because broadband channels experience frequency selective fading, the FDMA techniques can utilize both static and channel dependent scheduling to achieve multi-user diversity. The major problem in extending GSM TDMA and wideband CDMA to broadband systems is the increase in complexity with the multipath signal reception. The main advantage o f OFDM, as is for SC-FDMA, is its sturdiness against multipath signal propagation, which makes it suitable for broadband systems. SCFDMA has additional advantage of low Peak-to-Average Power Ratio (PAPR) compared with OFDM making it suitable for uplink transmission by user-equipment. 2. SYSTEM MODEL 2.1. MIMO Channel MIMO technology leverages multipath behavior by using multiple transmitters and receivers with an added ―spatial‖ dimension to increase performance and range. MIMO allows multiple antennas to send and receive multiple spatial streams at the same time. MIMO makes antennas work more efficiently by enabling them to combine data streams arriving from different paths and at different times to effectively increase receiver signal-capturing power. h11 x1 y1 x2 y2 : : : : : : xNt hNrNt yNr Fig.1 MIMO Channel with Nt transmitter and Nr receiver antenna International Journal of Electronics and Electrical Engineering ISSN : 2277-7040 Volume 2 Issue 2 http://www.ijecee. com/ https://sites.google. com/site/ijeceejournal/ 17 Spatial diversity technology is used by MIMO antennas. If there are more antennas than spatial streams, the additional antennas can add receiver diversity and increase range. Systems that use SISO can only send or receive a single spatial stream at one time. To implement MIMO either mobile device or access point need to support MIMO. A MIMO system can provide two types of gain: ̳spatial diversity gain‘ and ̳spatial multiplexing gain‘. Spatial diversity improves the reliability of communication in fading channels and spatial multiplexing increases the capacity by sending multiple streams of data in parallel through multiple spatial channels. Figure 1 describe about the MIMO channel where x1, x2,. xNt represent transmitted symbols and y1, y2, . yNr represent received symbols. A MIMO system with Narrowband MIMO channel can be represented by the following equation y = H*x + n (1) where y is the Nr × 1 received signal vector, and H is the Nr × Nt complex matrix of channel gains. Hij representing the gain from j th transmit antenna to i th receive antenna. x is the Nt × 1 transmitted signal vector, n is the Nr × 1 zero-mean complex Gaussian noise. H = UDV H (2) where U is an Nr ×Nr unitary matrix, D is an Nr × Nt non-negative diagonal matrix and V is an Nt ×Nt unitary matrix. (•) H is a Hermitian (conjugate transpose) operation. The diagonal entries of D are the nonnegative square roots of the eigen values of HH H , the columns of U are the eigenvectors of HH H , and the columns of V are the eigenvectors of H H H. We can rewrite Equation (1) using Equation (2) as y = UDV H x + n (3) Multiplying U H on both sides of Equation (3), it becomes U H y = U H UDV H x + U H n U H y = DV H x + U H n (4) Where n has the same statistical properties as n since U is a unitary matrix. Thus n is an Nr × 1 zero-mean complex Gaussian noise. For a wideband MIMO channel, the entire band can be subdivided into subcarriers. Then, the MIMO channel for each subcarrier becomes a narrowband MIMO channel. Let the entire band be subdivided into M subcarriers, then for k th subcarrier the entire band becomes a narrowband MIMO channel. Yk = Hk *Xk+ Nk (5) where Xk is the Nt ×1 transmitted signal vector, Yk is the Nr × 1 received signal vector, Nk is the Nr × 1 zero-mean complex Gaussian noise, and Hk is the Nr × Nt complex matrix of channel gains Hij, k representing the gain. Spatial diversity gain is the signal-to-noise ratio (SNR) exponent of the error probability and it corresponds to the number of independently faded paths. Alamouti transmit diversity scheme, and space-time coding are some known spatial diversity techniques. If spatial diversity is a means to combat fading, spatial multiplexing is a way to exploit fading to increase the data throughput. Space-time block coding (STBC) technique is used to transmit multiple copies of a data stream across a number of antennas. The transmitted signal must traverse a potentially difficult environment with scattering, refraction, reflection and then it may be corrupted by thermal noise in the receiver. So it implies that some of received copies will be better than others. In fact, space time coding combines all copies of received signal to extract information as much as possible. Alamouti transmit diversity scheme, and space-time coding are some known spatial diversity techniques. For a given MIMO channel, both diversity and multiplexing gains can be achieved simultaneously but there is a fundamental tradeoff between two gains. 2.2. SC-FDMA Signal Generation The transmitter and receiver structure of a SC-FDMA is illustrated in Fig. 1. The Transmitter is sending multiple block of data to a receiver. The input of transmitter and the output of the receiver are complex modulation symbols. LTE systems dynamically adapt the modulation technique to the channel quality, using Binary Phase Shift Keying (BPSK) in weak channels and up to 64-levelQuadrature Amplitude Modulation (64-QAM) in strong channels. The information block consists of M complex modulation symbols generated at a rate R source Symbols/second. Fig. 3 provides the details of the important elements of the transmitter in Fig.2. The Mpoint Discrete Fourier Transform (DFT) produces M frequency domain symbols that modulate M out of N orthogonal subcarriers spread over a bandwidth. (6) Where, is the subcarrier spacing. The channel transmission rate is, International Journal of Electronics and Electrical Engineering ISSN : 2277-7040 Volume 2 Issue 2 http://www.ijecee. com/ https://sites.google. com/site/ijeceejournal/ 18 (7) Bandwidth Spreading factor is given by: