Initial Uplink Synchronization Research Articles

Joint Initial Uplink Synchronization and Interference Aware Resource Allocation for D2D Communication in the MU-OFDMA System

ABSTRACT Over recent epoch, initial uplink synchronization has become an essential part of the wireless communication systems owing to its amenities in the identification of new users to originate communication. Yet, allocating and sharing resources to users is a bottleneck due to the interference caused by multiple users. Besides, preceding works didn't concentrate on the usage of an effective mechanism to estimate the parameters of the received signal in the multiuser synchronization environment. These downsides affect the throughput and spectrum efficiency of the designed OFDMA system. To address these bottlenecks, this paper proposes the Joint Initial Uplink Synchronization and Interference Aware Resource Allocation (JIUS-IRA) in the Multi-User OFDMA system. JIUS-IRA comprises four processes: Parameter Estimation, Optimum Antenna Selection, Resource Allocation, and Resource Sharing. Initially, JIUS-IRA executes the Fast Block Least Mean Square-based Parameters Estimation Scheme (FBLMS-PES) to estimate the user parameters. To reduce the power consumption during transmission between 5G MIMO base station and users, JIUS-IRA selects the optimal antenna for transmission. The Sign Rank Oriented Resource Allocation (SO-RA) method is executed to allocate sub-channel resources to the cellular user. The resource requirement of D2D users present in the OFDMA system is resolved via the Harris Hawks Optimizer based Resource Sharing Scheme (H2ORSS). The numerical results acquired from the simulation are highly confidential with regard to metrics Root Mean Square Error (RMSE) of timing estimation (∼0.006), RMSE of power estimation (∼0.0079), RMSE of frequency estimation (∼ 0.008), Throughput (∼95%), Spectrum Efficiency (∼11.9 bps), and Complexity (0.045 × 104).

A New Perspective on the Initial Uplink Synchronization Problem

We explore the frequency domain properties of the signal model associated with the initial uplink synchronization (IUS) problem, and provide some new insights. We show that the adverse effects of carrier frequency offset (CFO) are confined in a small region in the frequency domain. We present a new code design approach that avoids the above mentioned region to cancel the adverse effects of CFO. In this design the codes of different users occupy mutually disjoint intervals on the frequency axis. In this way we minimize the interference between different codes, and thereby, allow considerably large number of simultaneous IUS users in the system. For the proposed codes, we design a simple energy detector. This detector relies on classical results from statistical detection theory. We also propose a simple timing offset estimation technique, which requires us to locate the maximum in a periodogram. The resulting detection-estimation algorithms are simple, non-iterative, fast and accurate. The utility of the proposed design is illustrated using numerical simulation results.

Improved LTE like initial uplink synchronization via reduced problem dimension

Initial uplink synchronization (IUS) is a random access process in LTE that enables the eNodeB to detect, and uplink synchronize new user equipment. In future networks with huge number of devices, the number of simultaneous IUS users will increase significantly. In addition, it is desirable to serve users moving at high speed. We exploit the structure of the physical random access channel (PRACH) in LTE to reduce the dimension of the underlying data model. This reduction gives a very compact representation of channel impulse response (CIR). We utilize this representation to develop an efficient algorithm which can work in presence of large multiple access interference (MAI) and high carrier frequency offsets (CFO). When compared with the state of the art methods, the proposed method is capable of detecting a significantly higher number of IUS users and can allow high values of CFO. In addition, it produces very reliable estimates of both CIR and CFO of the detected users.

Fast Uplink Synchronization in LTE-Like Systems

We show a way to accelerate the successive multiuser detection (SMUD) algorithm for initial uplink synchronization (IUS) in an LTE-like system. We develop a new data model to pose IUS as a signal representation problem in a Fourier basis. We provide the theoretical guidelines for generating codes using the data model. Our method significantly reduces the complexity of computationally demanding multiplication steps of the SMUD algorithm.

Zadoff–Chu Sequence Design for Random Access Initial Uplink Synchronization in LTE-Like Systems

A Zadoff–Chu (ZC) sequence is uncorrelated with a non-zero cyclically shifted version of itself. However, this alone is insufficient to mitigate inter-code interference in LTE initial uplink synchronization. The performance of the state-of-the-art algorithms vary widely depending on the specific ZC sequences employed. We develop a systematic procedure to choose the ZC sequences that yield the optimum performance. It turns out that the procedure for ZC code selection in LTE standard is suboptimal when the carrier frequency offset is not small.

A Sparse Recovery Method for Initial Uplink Synchronization in OFDMA Systems

Initial uplink synchronization is an integral part of wireless communication systems. It enables the base station (BS) to detect new subscriber stations (SS) willing to commence communication. It also enables the BS to estimate the uplink channel parameters of these SSs. Accurate estimation of channel parameters is crucial, as they ensure the uplink signals from all the SSs arrive at the BS synchronously at similar power levels. However, this detection and estimation problem turns out to be very challenging when multiple users initiate the synchronization procedure at the same time. We address this issue by exploiting the underlying sparsity of the estimation problem. We propose a fast sparse signal recovery approach that shows a clear improvement in detection and estimation performance compared to other state-of-the-art methods. The proposed method can be integrated into any OFDM based standard.