Abstract:

In this paper, we propose a new approach that reduce the feedback amount with introducing a new condition when the number of sum of users that feedback don’t pass a predefined number (Max-users=K/L). Furthermore, we thought to enhance an equal chance among users to the feedback access with controlling the feedback access. Therefore, we suppose that each user feeds a single representational CSI code word back to the transmitter every L period of feedback in order to give an equal chance among users to the feedback access. We apply our proposal with “a per-user feedback” and with “a total feedback” in the opportunistic beam forming “OBF” and in ”the switched sub-codebook” techniques. Finally, simulations show that the proposed approach increases the capacity compared to the conventional approaches and gives good performances.

Abstract:

Orthogonal frequency division multiplexing OFDM/offset QAM (OQAM) system uses the isotropic orthogonal transform algorithm (IOTA) function, which has good localization properties in the time and frequency domains. This is employed instead of the guard interval used in a conventional OFDM/QAM system in order to be robust for multi-path channels. A comparative study of bit error rate (BER) under normal AWGN and multipath fading channel has been done between CP-OFDM and OFDM/OQAM with IOTA filter.

Abstract:

In this paper, we propose a channel estimation algorithm robust to the channel length effect with an adaptive guard interval technique for LTE Downlink systems. As LTE Downlink system is based on a MIMO-OFDMA technology, a Cyclic Prefix (CP) is inserted at the beginning of each transmitted OFDM in order to mitigate both inter-carrier interference (ICI) and inter-symbol interference (ISI) caused by the multi-path propagation. Usually, the length of the inserted cyclic prefix is defined to be equal to or longer than the channel length. However, and due to some unforeseen channel behavior, the cyclic prefix can be shorter than the channel length. Therefore, we have proposed a hybrid channel estimation technique able to resist to the length effect. However, the proposed algorithm suffers from the presence of ISI. Moreover, LTE Downlink bandwidth suffers from a loss factor given by the insertion CPs and the insertion of pilot signals in order to estimate the channel. In this paper, we propose a hybrid channel estimation technique with an Adaptive Guard Interval Length (AGIL) in order to enhance the performance of the system and improve the LTE Downlink bandwidth efficiency. MATLAB Monte–Carlo simulations are used to evaluate the performance of the proposed estimator in terms of Bit Error Rate (BER) for 2x2 LTE Downlink systems.