Sharif Digital Repository

In this study, a two-user discrete memoryless multiple-access channel with two correlated states known non-causally at the corresponding encoder is considered. Each encoder transmits a message independent of the other encoder's and tries to cooperate with it. To consider cooperative encoders, it is assumed that each encoder strictly-causally receives and finds out the other encoder's transmitted signals and tries to cooperate with the other encoder by transmitting its message. A special case is also studied in which the common part of the states is known at the both encoders, resulting in a larger rate region. For these two scenarios, achievable rate regions are derived using a combination... 

The two-user discrete memoryless state-dependent multiple-access channel with cooperating encoders is considered. It is assumed that the channel is controlled with two independent states such that each of the channel state information is noncausally available at one encoder. Moreover, based on the intrinsic characteristic of wireless networks, it is assumed that each encoder strictly causally receive a noisy version of the transmitted signal of the other encoder. Hence, the encoders can cooperate in transmitting the message to the receiver. An achievable rate region for the channel is derived by use of rate splitting, block Markov encoding and Gelfand-Pinsker multilevel encoding along with... 

We consider a model of a bosonic memory channel, which induces correlations among the transmitted signals. The application of suitable unitary transformations at the encoding and decoding stages allows the complete removal of correlations, thereby mapping the memory channel into a memoryless one. However, such transformations, being global over an arbitrarily large number of bosonic modes, are not realistically implementable. We then introduce a family of efficiently realizable transformations, which can be used to partially remove correlations among errors, and we quantify the reduction of the gap with memoryless channels  

Employing femtocell technology noticeably improves both the indoor coverage and the overall cellular network's capacity. In the downlink scenario, when macrocell users (MUs) are far from the macro base station (MBS) and close to the femto access points (FAPs), the transmitted signals of FAPs to their users cause severe interference on MUs. One solution to overcome this issue is serving MUs by neighbouring FAPs. Generally femtocells are selfish and have no desire to allocate their resources to MUs. In this study, a framework to motivate femtocells to share their free resources with MUs is proposed. In this framework, the femtocells are assumed to belong to a specific unit. The unit encourages... 

A multiple input multiple output (MIMO) radar system, unlike a conventional phased array radar, can choose freely the signals which transmitted via its antennas to maximize the power around the locations of the specific targets, or more generally to approximate a given transmit beampattern, and also to minimize the cross-correlation of the signals reflected back to the radar by the targets of interest. In this paper we use of phase-coded signals and show how the above desirable features of MIMO radars with some operational consideration can help us to have a desire beampattern. We suppose that for a collection of phase-coded signals, the elements of transmitted signals cross-correlation... 

In this paper a sub-optimal control technique is proposed for a linear Gaussian system with a few distributed interacting sub-systems. Controller of each sub-system has only access to its own measurement and a noisy version of measurement and control vectors of other sub-systems that are communicated through an Additive White Gaussian Noise (AWGN) communication network. The power to be allocated to each transmitter antenna is calculated so that the received signal is the transmitted signal plus additive white Gaussian noise. Under some conditions it is shown that the proposed sub-optimal control technique results in bounded mean square stability. The satisfactory performance of the proposed... 

In this paper, it is shown that some spikes exist in power spectral density (PSD) of ultra-wideband-time-hopping-pulse-position-modulation (UWB-TH-PPM) transmitted signal. Analytical and numerical simulation results show that these spikes severely degrade UWB-TH-PPM system bit-error-rate performance and must be properly removed. This paper proposes a novel multi-access scheme that uses both direct-sequence (DS) and time-hopping (TH) multi-access schemes to remove these harmful spikes. Analytical and numerical simulation results show that the proposed scheme removes the spikes from the PSD of the UWB-TH-PPM transmitted signal and yields better performance. In this paper, the performance of... 

A novel low-complexity detection scheme is proposed for the multiple-input multiple-output (MIMO) single-carrier frequency division-multiple access (SC-FDMA) systems, which is suitable for ASIC implementations. The proposed detection scheme makes an initial estimate of the transmitted signal based on a minimum mean square error (MMSE) frequency domain equalizer (FDE) detector and finds symbols with higher error probability among them and browse more candidates for them in the constellation to improve their initial estimate. Based on this approach, architecture is introduced that achieves superior bit error rate (BER) performance compared to the conventional MMSE FDE. The performance of the... 

A simulation tool, based on Ray Tracing method, has been developed and validated for millimeter-wave band. This tool helps for predicting the signal level as well as the delay characteristics of a propagation channel. Since the resultant of the received replicas of the transmitted signal at receiver point can experience a deep fade and consequently the quality degradation, a proper diversity method can effectively alleviate this drawback. Using this simulation tool and extracting the received wave characteristics in a street scenario, an analytical expression for predicting the space diversity gain for the Selection Combining technique and Maximal-Ratio Combining technique has been proposed  

Orthogonal frequency division multiplexing (OFDM) is one of the widely used multiplexing techniques in wireless communications and especially cognitive radio networks. One of the key challenges of this technique is its high peak to average power ratio (PAPR) of the transmitted signal. This paper, introduces a new approach to PAPR reduction of OFDM signals using harmony search algorithm (HSA) based on the partial transmit sequence (PTS) method. The simulation results demonstrate that the proposed algorithm has better PAPR reduction performance as an accurate and low complexity approach for OFDM systems