This paper proposes frequency domain precoding vector switching (PVS) transmit diversity for synchronization signals to achieve fast physical cell identity (PCID) detection for the narrowband (NB)-Internet-of-Things (IoT) radio interface. More specifically, we propose localized and distributed frequency domain PVS transmit diversity schemes for the narrowband primary synchronization signal (NPSS) and narrowband secondary synchronization signal (NSSS), and NPSS and NSSS detection methods including a frequency offset estimation method suitable for frequency domain PVS transmit diversity at the receiver in a set of user equipment (UE). We conduct link-level simulations to compare the detection probabilities of NPSS and NSSS, i.e., PCID using the proposed frequency domain PVS transmit diversity schemes, to those using the conventional time domain PVS transmit diversity scheme. The results show that both the distributed and localized frequency domain PVS transmit diversity schemes achieve a PCID detection probability almost identical to that of the time domain PVS transmit diversity scheme when the effect of the frequency offset due to the frequency error of the UE temperature compensated crystal oscillator (TCXO) is not considered. We also show that for a maximum frequency offset of less than approximately 8 kHz, localized PVS transmit diversity achieves almost the same PCID detection probability. It also achieves a higher PCID detection probability than one-antenna transmission although it is degraded compared to the time domain PVS transmit diversity when the maximum frequency offset is greater than approximately 10 kHz.

This paper deals with a beamforming and cell ID detection technique for a mobile station (MS) with multiple antenna arrays in millimeter wave (mm-wave) cellular communication systems. Multiple antenna arrays, required to cover the entire space around the MS, can be used to estimate the direction of arrivals (DoAs) and cell IDs, form beams in the direction of DoAs, select a serving cell in a cooperative manner, and improve BER performance by signal combining. However, a signal may enter the overlapped region formed by two adjacent arrays in the MS, resulting in a double-counting problem during the cell searching period. In this paper, a beamforming and cell detection technique without double-counting is proposed to handle this problem, and they are evaluated by simulation in a simple scenario of an mm-wave cellular system with spatial channel model (SCM).

This paper presents the effect of transmit diversity on the initial and neighboring cell search time performance and the most appropriate transmit diversity scheme based on system-level simulations employing synchronization signals for the Long Term Evolution (LTE) downlink. The synchronization signals including the primary synchronization signal (PSS) and secondary synchronization signal (SSS) are the first physical channel that a set of user equipment (UE) acquires at the initial radio-link connection. The transmit diversity candidates assumed in the paper are Precoding Vector Switching (PVS), Cyclic Delay Diversity (CDD), Time Switched Transmit Diversity (TSTD), and Frequency Switched Transmit Diversity (FSTD), which are all suitable for simple blind detection at a UE. System-level simulation results show that transmit diversity is effective in improving the detection probabilities of the received PSS timing and PSS sequence in the first step and those of the SSS sequence and radio frame timing in the second step of the cell search process. We also show that PVS achieves fast cell search time performance of less than approximately 20ms at the location probability of 90% regardless of the inter-cell site distance up to 10km. Hence, we conclude that PVS is the best transmit diversity scheme for the synchronization signals from the viewpoint of decreasing the initial and neighboring cell search times.

In this paper, a new technique is proposed to reduce the frequency of cell search by user equipment (UE) in the presence of femtocells. A new common signal (CS) and a separate set of primary synchronization signals (PSSs) are employed to facilitate efficient cell search in a next-geration LTE-based system. The velocity of the UE is also utilized to determine cell search mode. A slow UE recognizes the presence of femtocells using the CS, so that it can make separate searches for macrocells and femtocells. A fast UE will not search for femtocells since the coverage of femtocells is restricted to a small region. The fast UE detects the macrocell boundary using the PSSs transmitted from neighboring macrocells, so that it can search for macrocells only at the macrocell boundary. The effects of CS and UE velocity on the number of cell searches are analyzed. The performance of the proposed technique is evaluated by computer simulations.

Initial cell search in wideband code-division multiple-access (W-CDMA) systems is a challenging process. On the one hand, channel impairments such as multipath fading, Doppler shift, and noise create frequency and time offsets in the received signal. On the other hand, the residual synchronization error of the crystal oscillator at the mobile station also causes time and frequency offsets. Such offsets can affect the ability of a mobile station to perform cell search. Previous work concentrated on cell synchronization algorithms that considered multipath channels and frequency offsets, but ignored clock and timing offsets due to device tolerances. This work discusses a robust initial cell search algorithm, and quantifies its performance in the presence of frequency and time offsets due to two co-existing problems: channel impairments and clock drift at the receiver. Another desired performance enhancement is the reduction of power consumption of the receiver, which is mainly due to the computational complexity of the algorithms. This power reduction can be achieved by reducing the computational complexity by a divide and conquer strategy during the synchronization process.

In this paper, cell searching and direction-of-arrival (DoA) estimation methods are proposed for mobile relay stations with a uniform linear arrays in OFDM-based cellular systems. The proposed methods can improve the performance of cell searching and DoA estimation, even when there exist symbol timing offsets among the signals received from adjacent base stations and Doppler frequency shifts caused by the movement of the mobile relay station. The performances and computational complexities of the proposed cell searching and DoA estimation methods are evaluated by computer simulation under a mobile WiMAX environment.

We propose a new majority voting scheme for identifying downlink primary scrambling code, where two voting processes with different coherent correlation intervals (CCIs) are simultaneously performed. A false alarm probability and a threshold adjustment for the proposed scheme are investigated, and it is shown by computer simulations that the proposed scheme can perform well over a wide range of frequency offsets.

A differential cross-correlation cell ID identification algorithm is proposed for IEEE 802.16e OFDMA cellular system. The cell ID represents the number of the preamble selected by the base station in downlink mode. First, we construct the downlink (DL) preamble structure and signal model with carrier frequency offset (CFO) and channel effects. Next, in order to achieve the initial synchronization, a differential receiver with cross correlation for all preamble patterns is proposed to search for cell ID. Simulation results confirm that the proposed structure is suitable for ITU fading channels and outperforms the conventional cell search system.

In this paper, we propose an AGC (Automatic Gain Control) algorithm for initial cell search in 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) TDD (Time Division Duplex) system. Since the received signal has a large signal power difference between uplink and downlink subframe in wireless communication systems using a TDD scheme, conventional AGC scheme cannot sufficiently adjust the AGC gain because the AGC gain cannot converge fast enough to properly respond. Therefore, conventional AGC scheme leads to increased AGC gain variation, and the received signal will be attenuated by large AGC gain variation. To overcome this limitation, we propose an AGC scheme based on the average amplitude ratio calculation which can not only effectively increase convergence speed of the AGC gain but also maintain the stability of AGC operation in LTE TDD system. Also, it is important for AGC to converge efficiently for the accurate radio frame timing detection during the subsequent initial cell search procedure. Therefore, we also consider the proposed AGC scheme in combination with PSS (Primary Synchronization Signal) detection interface for the first step of initial cell search process in LTE TDD system to obtain both a stable AGC operation and accurate PSS detection performance. By extensive computer simulation in the presence of frequency offset and various channel environments, we verified that the proposed method can obtain a good behavior in terms of demodulation and PSS detection performance in LTE TDD system.

OFDM (Orthogonal Frequency Division Multiplexing) is widely used in wideband wireless communication systems due to its excellent performance. One of the most important operations in OFDM receivers is preamble detection. This paper addresses a general form of extended differential detection methods, which is a combination of differential detection and a moving average filter. This paper also presents a filter size determination method that achieves satisfactory performance in various channel environments.

The 3GPP Long Term Evolution Advanced (LTE-A) system, as compared to the LTE system, is anticipated to include several new features and enhancements, such as the usage of channel bandwidth beyond 20 MHz (up 100 MHz), higher order multiple input multiple output (MIMO) for both downlink and uplink transmissions, larger capacity especially for cell edge user equipment, and voice over IP (VoIP) users, and wider coverage and etc. This paper presents some key enabling technologies including flexible uplink access schemes, advanced uplink MIMO receiver designs, cell search, adaptive hybrid ARQ, and multi-resolution MIMO precoding, for the LTE-A system.

This paper presents a comparison of hierarchical and non-hierarchical synchronization channel (SCH) structures in terms of the initial cell search time and neighboring cell search time in order to establish the optimum SCH structure in the Evolved UTRA downlink. Computer simulation results show that in a 19-cell configuration, the cell search time at 90% in the cumulative distribution function (CDF) using the hierarchical SCH structure is less than half that using the non-hierarchical SCH structure in a neighboring cell search under low signal-to-interference plus noise power ratio (SINR) conditions, although both structures achieve almost the same cell search time in the initial cell search. This is due to the cross-correlation based SCH symbol timing detection in the hierarchical SCH structure, which is affected less by noise than the auto-correlation based detection in the non-hierarchical SCH structure. Thus, we conclude that the hierarchical SCH structure is superior to the non-hierarchical SCH structure based on the cell search time performance especially in the neighboring cell search.

This letter proposes a fast carrier search method, the Carrier Search Step method (CSSM), to quickly detect the carrier frequency even when mobile stations have no knowledge of the carrier frequencies used [1]. CSSM consists of two operations: 1) mobile stations use the coarse-to-fine search to detect the synchronization channel (SCH), and 2) the center frequency of SCH is shifted within the channel bandwidth so that mobile stations can detect the SCH in an early step of the coarse-to-fine search. Compared with conventional methods, CSSM can reduce carrier search time by 90% when SCH bandwidth is 1.08 MHz and the channel bandwidth is 5 MHz. The reduction in carrier search time strengthens as the channel bandwidth increases.

In this letter, a mobile relay station (MRS) for vehicles with beamforming antennas is considered to increase the reliability of transmission link, especially for the MRS at cell boundary. Joint methods for cell searching and DoA estimation are proposed to form a beam in the direction of target BS while nulling interferences from adjacent BSs, especially for IP-based cellular systems employing break-before-make handover or make-before-break handover. The proposed cell searching and DoA estimation methods are evaluated by computer simulation under the environment of IEEE 802.16e (WiBro).

This paper proposes physical channel structures and a cell search method for OFDM based radio access in the Evolved UTRA (UMTS Terrestrial Radio Access) downlink, which supports multiple scalable transmission bandwidths from 1.25 to 20 MHz. In the proposed physical channel structures, the central sub-carrier of the OFDM signal is located on the frequency satisfying the 200-kHz raster condition regardless of the transmission bandwidth of the cell site. Moreover, the synchronization channel (SCH) and broadcast channel (BCH), which are necessary for cell search, are transmitted in the central part of the entire transmission spectrum with a fixed bandwidth. In the proposed cell search method, a user equipment (UE) acquires the target cell in the cell search process in the initial or connected mode employing the SCH and possibly the reference signal, which are transmitted in the central part of the given transmission bandwidth. After detecting the target cell, the UE decodes the common control information through the BCH, which is transmitted at the same frequency as the SCH, and identifies the transmission bandwidth of the cell to be connected. Computer simulations show the fast cell search performance made possible by using the proposed SCH structure and the cell search method.

In this letter, a method estimating the intercell carrier frequency-offset (CFO) in orthogonal frequency division multiplexing (OFDM)-based cellular systems is proposed for the user's equipment (UE), especially at the cell boundary, in downlink channels. After describing a new method of deriving the intercell CFO from the signals received by adjacent base stations (BSs), we propose a cell-searching method using the estimated CFOs. It is shown by computer simulation that the proposed methods can uniquely estimate the intercell CFOs and identify the target BS with a high detection probability at the UE.

A cell search technique utilizing a known postfix for OFDM (orthogonal frequency division multiplexing) cellular systems is described. The known postfix is generated in the time domain by inserting pilots in the frequency domain and plays the role of the cyclic prefix in general OFDM systems. Since it demonstrates good correlation properties, it can be facilitated to synchronize each symbol with an identified postfix. In this paper, two different known postfixes are allocated to each cell. One is used for cell identification and symbol synchronization, which is designed to be different among neighboring cells. The other is used for frame synchronization and is the same for all cells. In the simulation, the cell search is accomplished with a probability greater than 10-3 at -27 dB in a vehicular channel. Even at -30 dB, the cell search probability is greater than 10-2 in a pedestrian channel as well as 10-3 in the AWGN (additive white gaussian noise) channel.

In this letter, a pilot structure and an efficient algorithm for downlink synchronization and cell searching in OFDM-based cellular systems are proposed. The pilots, randomly allocated in the frequency domain, allow us to minimize inter-cell interference (ICI) as well as to increase cell searching capability, estimation range of integer carrier frequency offset (CFO), and estimation accuracy of symbol timing offset (STO). The proposed low-complexity joint algorithm for integer CFO estimation, cell searching, and downlink detection is robust to ICI, multipath channel, STO and fine CFO.

For three-step cell search in WCDMA, a stepwise serial scheme is conventionally employed, where each step of cell search operates in serial. In order to reduce the cell search time, a stepwise parallel scheme can be considered as a candidate for cell search, where each step operates in pipelined fashion. However, in the parallel scheme where the processing time in every step is equal, excessive accumulations are caused in step (1) and step (3) because the period of a code used for step (2) is much longer than that for the other steps. And it does not provide any gain because the effect becomes easily saturated with the number of accumulations. In this paper, the performance of parallel cell search is analyzed, and compared with that of serial cell search. Finally, it is shown that the performance of parallel cell search can be improved by adjusting the processing time in each step, based on the analytic results.

This paper proposes a new cell-specific scrambling code (CSSC) assignment method and a fast cell search algorithm in the forward link for Orthogonal Frequency and Code Division Multiplexing (OFCDM) wireless access that are suitable for a system incorporating coexisting isolated and cellular cells. In the proposed method, one or some CSSC groups and thereby the CSSCs belonging to the CSSC groups are exclusively assigned to isolated cells. By detecting the best CSSC assigned to an isolated cell with higher priority than the cellular cells, the best cell including the isolated cell obtaining the minimum path loss can be detected far faster than by using the conventional cell search method, which employs uniform CSSC assignment. Computer simulation results show that by using the proposed cell search method together with the exclusive CSSC assignment to the isolated cells, the isolated-cell detection probability of approximately 90% is achieved at the cell boundary after the cell search time of 10 msec, while corresponding detection probability using conventional CSSC assignment is approximately 80% without notifying the user equipment of the cell type and its CSSC information of the surrounding cells via the broadcast channel, at the average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) of 10 dB for the common pilot channel (CPICH) in the cellular cells, when the transmission power ratio of the CPICH to the packet data channel (PDCH) for a one-code channel is RCPICH = 9 dB in a 20-cell layout model.