Random Access Design for UMTS Air-Interface Evolution
ABSTRACT Comprehensive long term evolution of the Universal Mobile Telecommunications System (UMTS) specifications is currently ongoing to provide significant improvement over the current release. Important goals for the evolved system include significantly improved system capacity and coverage, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operations and seamless integration with existing systems. To ensure low latency, users must be able to establish a connection to the network quickly. This paper provides a preliminary design and procedure for the random access channel used to establish a connection when the mobile is not yet time-synchronized to the network in the uplink.
Conference Paper: Timing synchronization method for device-to-device communication system[Show abstract] [Hide abstract]
ABSTRACT: In this paper, we propose a timing synchronization method for device-to-device (D2D) system. In the past several years, many synchronization protocols have been investigated for ad-hoc network system. However, it is difficult to apply them to D2D system directly because of some difficulties. In D2D system, these protocols have some structural limitations and might show inefficient performance, because cellular base station can be employed to D2D network to enhance performance and reduce resources. Also, D2D network should be able to support a variable number of devices. Therefore, in this paper, we propose a new timing synchronization method for D2D system. In the proposed method, synchronization can be achieved in different ways according to the existence of available cellular base station. In the proposed method, we first consider cellular-assisted (CA) method based on random access process in cellular uplink procedure. On the other hand, when cellular base station is not available, user equipment performs stand-alone (SA) method. In SA-D2D, three step synchronization process and a new reference clock decision rule are proposed. We verify that the proposed method can achieve high accuracy synchronization in a short period.Proceedings of the 7th International Conference on Ubiquitous Information Management and Communication; 01/2013
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ABSTRACT: Recently, 3rd generation partnership project has adopted a new study item for device-to-device (D2D) communication service in long term evolution (LTE) system, called the group communication system enablers for LTE (GCSE_LTE). In GCSE_LTE, synchronization is an important issue; therefore, many synchronization methods of wireless sensor network and ad-hoc network can be considered. In these conventional methods, they only consider synchronizing the transmission time of signal. However, in case of ideal synchronization method, conventional methods cause a link delay spread (LDS) problem. LDS means a time difference between received signals which are caused by the different propagation delays among user equipments (UEs). The problem is that all UE need an extra length of cyclic prefix (CP) to receive multi-path delayed signals, and it can be a substantial resource waste. Therefore, in this paper, we propose a fine timing synchronization method by a master node which can reduce the maximum LDS in D2D group. We verify that the proposed method can reduce the average length of additionally required CP compared to conventional methods.2013 19th Asia-Pacific Conference on Communications (APCC); 08/2013
Conference Paper: Enhanced preamble detection for PRACH in LTE[Show abstract] [Hide abstract]
ABSTRACT: The performance of preamble detection in Physical Random Access Channel (PRACH) for long term evolution (LTE) and its advanced degrades when channels become more time dispersive, such as Extended Typical Urban (ETU). However, the Base Station (BS) target received power is determined by users with time dispersive channels, in order to keep the acceptable performance for most of users in a cell. Motivated by the idea of collecting the energy of multiple paths, the optimal statistic is derived in this paper given the Power Delay Profile (PDP) of Rayleigh fading channels. An analytical framework of performance is also proposed in this paper and verified by simulation. It is shown that the proposed optimal statistic increasingly outperforms the traditional peak detecting when time-dispersion of channels increases. Considering the difficulty of achieving the accurate PDP in some scenarios, a suboptimal but robust solution is further developed. Compared with peak detecting, the suboptimal solution lowers the BS's target received power by over 1.1dB for Format 0 PRACH with both 2 and 4 receive antennas in the ETU channel, significantly reduces the user's power consumption and improves the LTE PRACH coverage.Wireless Communications and Networking Conference (WCNC), 2013 IEEE; 01/2013