Performance Evaluation of Orthogonal Space- Time Block Code (Costs) Concatenated with Trellis-Coded Modulation (Etc) over a IMO Fading Channel BY costal Performance Evaluation of orthogonal space-time block code (COSTS) concatenated with trellis-coded modulation (ETC) over a IMO Fading Channel Abstract Orthogonal Space-time block coding (COSTS) is a technique used in wireless communications to transmit multiple copies off data stream across a number of antennas and to exploit the various received versions of the data to improve the reliability of data-transfer. But this technique suffers from decrease in coding gain.

While Trellis coded modulation (ETC) is a technique which combines coding and modulation to achieve significant coding gains without comprising bandwidth efficiency. In this project, I would like to employ a concatenated COSTS with Trellis- coded modulation in a IMO fading Channel and vary the number of antennas in the transmitter and receiver side and observe the performance of the system. This technique improves the coding gain of the system. All comparisons and analyses are done by writing MUTUAL scripts for the proposed coding schemes. INTRODUCTION In wireless communication, fading channels cause degradation in transmitted signals.

One useful method to reduce the adverse effects of fading channels is to employ diversity. When the same transmitted information is transmitted on several more or less independently fading channels it creates diversity, and is exploited by combining resulting received signals. Diversity can in general be achieved by creating independent channels in time, frequency, or space. Orthogonal transmit diversity, such as frequency and time diversity, have some properties that are quite attractive in wireless communication as they can provide a diversity gain without the need of multiple transmit/receive antennas.

However, this causes either an increase in bandwidth or time n De in transmitting the intimation C Witness introduced the bandwidth efficient transmit diversity scheme [3] which transmits the same information from both antennas simultaneously and delay one symbol interval. After that, Throat proposed a new method, namely Space-Time Trellis Codes (EST.) [4, 5], EST. is Joining the channel coding with trellis encoder, modulation, and diversity. The decoding complexity at the receiver increases exponentially with the number of trellis states and transmission rate when number of transmit antennas is fixed.

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To decrease the decoding complexity of EST., the first Space Time Block Code (STAB) was proposed by Almost over two transmit antennas and two time periods in [5] . And then Throat developed the Alimony’s STAB with more antennas at both transmitter and receiver in [6]. STAB can achieve advantages about the full diversity gain with no penalty in given bandwidth, and the encoding and decoding of these codes have less complexity than EST.. But STAB do not perform perfectly for a coding gain[7] .

Thereby, the concatenation of these code with outer code such as Block-coded Modulation (BCC) or Trellis-coded Modulation (ETC) is an appropriate solution to combine the very easy decoding structure of the STAB with an additional coding gain and diversity gain [8]. For the systems with large number of transmit antennas and high bandwidth efficiency, the receiver may become too complex. To solve this problem, some methods were proposed such as Layered Space-Time Codes in [9] and Combined Array Processing with Space-Time Coding in [10] and [4]. The report is organized as follows.

In section 2, the basic principle of STAB is reviewed. Sections 3 presents a brief review about ETC. In section 4 a brief introduction to the different noise present in the channel was considered section 5 discusses the concatenated scheme and the system model. In section 6, frame-error rate performance of the basic ETC, and STAB are simulated separately as well as the concatenated of STAB over IMO fading channels are evaluated through a program in MUTUAL script. Section 7 present the outcome performance of these systems, and concluding remarks are provided in section 8.

SPACE TIME BLOCK CODED SYSTEM A general IMO system considered with TN transmit antennas and TRY receive antennas. At the input of the Space Time encoder Block a n- dimensional vector x=[xx,xx, …. CNN]T with elements from a certain complex signal constellation with M=mm symbols. The output signals obtained is a matrix code word of size Twixt . During each tit time slot, the symbols gig are sent simultaneously from transmitting antennas ,2,… TN . For each lath transmit antenna, symbol gig are sent successively at time slots.

For this reject a particular type of space time block code called as Orthogonal Space Time Block Code (COSTS), for which the transmission (1) In the first time slot the symbols XSL are transmitted simultaneously trot the two transmit antennas and and are transmitted simultaneously in the second time slot. Both symbols XSL and xx are spread over two transmit antennas and over two time slots. The transmitter does not have information about the channel thus it is assumed that each antenna has equal transmit power.

TRELLIS – CODED MODULATION ETC is a modulation scheme is used in band limited channels such as telephone nines as it allows highly efficient transmission of information. Trellis modulation was invented by Gottfried Ungenerous [1]. The functions of a ETC consist of a Trellis Code and a Constellation Mapped as shown in Figure 1 . The functions of the convocational coder of rate: and a M-ray signal mapped is combined in this type of modulation and it maps M=k input points into a larger constellation of M=k+1 constellation points. Atria G satisfy the conditions [1 1]: linearity: all elements gig are linear combinations of the input symbols and their orthogonally: conjugates; Ill (l then CNN identity matrix. K bits CONVOLUTE ‘ANAL ODDER Rate k/K+l k+l bits M-ASK Modulator I I ) Where II is the Euclidean norm and In is M-ASK SMB Los COSTS provides full diversity and a very simple ML decoding scheme but its main disadvantage is that it does not provide additional coding gain. To increase the coding gain further, a high performance outer code has to be concatenated with an appropriate STAB used as an inner code. A.

The Almost Code The simplest transmit diversity scheme for two transmit antennas is the Almost code and it has been implemented for this project. It is considered that the umber of transmit antennas are two, the number of time slots are two and the number of input symbols are two. Figure 1 : General Trellis Coded Modulation[l]. CHANNELS Wireless transmission uses air or space for its transmission medium. The radio propagation is not as clean as in wire transmission since received signal comes from the transmitter along with a combination of reflected, diffracted, and scattered versions of the transmitted signal.

Secondary waves occur when the signal is obstructed by sharp objects causing diffraction. When signal impinges on rough surface it causes scattering. The receiver chives more than one copy of the signal in multiple paths with different powers as the received signal will contain scattering wave whose energy is spread in all directions. Reflection, diffraction and scattering in combination give birth to multipart fading[12]. A. GANG Channel Additive white Gaussian noise (GANG) channel is a universal channel model for analyzing modulation schemes[13]. For this project GANG channel has been implemented as the receiver noise.

The GANG for this project is used to add whit Gaussian noise to the transmitting signal . It is inferred that its amplitude frequency espouse is flat (infinite bandwidth) and phase frequency response is linear for all frequencies so that modulated signals pass through it without any amplitude loss. GANG only introduces distortion. Received signal can be simplified to: r(t)=s(t) + n(t) where n( ) I EAI dative Gaussian noise[12 B. Raleigh Fading Channel Constructive and destructive nature of multipart components in flat fading channel can be approximated by Raleigh distribution if there is no direct path between transmitter and receiver.

The received signal can be simplified to: r (t)=s(t)*h(t) +n(t) (3) Where h (t) is the random channel Atria having Raleigh distribution and n(t) is the additive Gaussian noise. The Raleigh distribution is basically the magnitude of the sum of two equal independent orthogonal Gaussian random variables and the probability density function given by: Where is the time-average power of the received signal [14, 15]. V. CONCATENATED COSTS AND ETC – SYSTEM MODEL To combine the benefit of STAB and the ETC, Concatenation is also frequently employed in space- time coded systems.

Here, the outer code is frequently a ETC system whose symbols are transmitted via an inner space-time coded system el COSTS. 16] A. Trellis Coded Modulation Encoder In the ASK ETC Encoder block, encoding is done by a convolution encoder and the results are mapped into a ASK signal constellation. The output from the encoder is a frame based complex vector. Using Mutual trellis function, for an 8 state 8 ASK trellis different trellis structures are designed by using the ” next state” and “output state” parameters.

The constellations are partitioned into cossets to maximize the minimum distance between pair of points in the same group through this modulation technique. This modulation technique is programmed into truncated ode where encoder state are reset to all zeros occurs at the start of every frame . The type of output for the block is set to be double. B. ASK ETC Decoder The ASK ETC Decoder block uses the Biter Algorithm [17] to decode a trellis-coded modulation (ETC) signal that was formerly modulated using a ASK signal Constellation.

The Trellis structure in this block should equal to that in the ASK ETC Encoder block, to guarantee accurate decoding. The output of the COSTS Combiner is a frame-based column vector is the input signal to this block. Decoder block’s output s a frame-based binary column vector whose length is k times the vector length of the input signal[17] As the input signal length is 50 t gives output as 2 which is equal to 100. The Operation mode factor is set to Truncated to treat each frame separately. The Trace back depth parameter, D is set to 30.

The trace back path starts at the state with the lowest metric. D must be less than or equal to the vector length of the input and 5 6 times greater than the constraint length of the ETC. As the length of the input is 50, and constraint length is 3, D is taken as 30 to make sure an almost lossless performance. C. COSTS Encoder In this block encoding is done by meaner of orthogonal space-time block code(COSTS). The input symbols are mapped block-wise and it concatenates the output code word matrices in the time domain. Almost code [6] is used in this encoder block to encode the information symbol.

Figure 2 : Block Diagram of a concatenated COSTS and ETC scheme . D. COSTS combiner The COSTS combiner block takes the input signals from the receiving antennas. The input signals and the channel state information is combined to give encoded signal information. In the combiner, the operation is done separately for each symbol. The parameters that these operations depend on are the number of transmission antennas and the coding rate. E. IMO channel model Different antenna configurations are designed in this IMO channel model to increase the diversity gain of the system.

A ISIS (1 1, antenna configuration) is also given for comparison. In this model Multipart Raleigh Fading Channel blocks are used. During simulation Additive White Gaussian noise (GANG) is added at the receiver side Figure 4 : Comparison of the concatenated scheme with only COSTS or ETC Figure 3 : FEAR vs. SON plot for Trellis coded Modulation in a ISIS system f IMO systems with COSTS scheme SIMULATION Figure 5 : Comparison For this project, a ISIS system (XIX antenna configuration) for a ETC and a IMO system with ex. transmit-receive antenna was modeled for COSTS and the concatenated COSTS and ETC.

Frame Error Rate is the ratio of data received to total data received per frame. FEAR is calculated by comparing the original source bit with the decoded bit got from the ETC decoder. The maximum number of frame was taken as xx and number of error frames was taken to be 200. The system was modeled using MUTUAL software (script). Evil. RESULT The sound noise ratio versus frame error rate plot of a trellis modulation in a ISIS system (Figure 3) is used as the reference as it is the encoded signal. Figure 4 shows the comparison between the concatenated scheme, COSTS and ETC.

ETC scheme is used as a base reference. It can be clearly deciphered that for the desired range of SON, COSTS does not have a good coding gain while the concatenated scheme shows a good improvement in the coding gain while compared to COSTS. Figure 5 shows a comparative study of COSTS response to the change in the number of antennas in receiver and transmitter side. It shows that it has a moderate diversity gain but when compared to the diversity gain of the concatenated scheme, the concatenated scheme NAS a greater more improved diversity gain.

It also can be deciphered that greater the number of antennas the lesser the frame error rate. Vial. CONCLUSION In this work, a concatenated scheme of Scoots and ETC has been studied which is a good scheme for future wireless communication systems. Its diversity performance for different number of antennas in the receiver and transmitter side has been compared with different schemes. Further scope of study can be on the optimal rallies design for higher state ETC as we coding gain increases with higher trellis state.


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