Showing papers by "Sequans published in 2009"

Method and system for memory management in a HARQ communications system

Abstract: A method is provided for memory management in a communications system using a HARQ error control mechanism, in which a transmitter establishes a plurality of HARQ channels with a receiver. The method includes determining whether each received encoded HARQ packet needs to be combined with an encoded HARQ packet already stored in HARQ memory. In case a received encoded HARQ packet does not need to be combined, the method determines whether there is a free memory space available in the HARQ memory for storing that received encoded HARQ packet, and if so, allocating that free memory space for storage of that received encoded HARQ packet. If not, the method determines whether a certain amount of memory space can be forced to be freed, and if so, de-allocates it and then allocates it for storage of that received encoded HARQ packet, that packet is sent to an FEC decoder.

Method and system for radio access technology monitoring in a wireless communications system

Abstract: A method and apparatus are provided for radio access technology (RAT) monitoring, in a wireless system environment having wireless communications equipment and at least two different RATs that coexist for providing to the equipment access to one or more communications networks. The equipment has at least two subsystems, each adapted for establishing and maintaining an active communications connection with a certain one of the different RATs. The equipment selects at least a first RAT, among all the RATs available in a certain geographical area, for establishing the active communications connection, according to a monitored characteristic of the first RAT. The method includes scanning a characteristic of a second RAT available for communication in the geographical area while the equipment maintains an active communications connection with the first RAT, and performing the scanning step when the equipment does not transmit signals through the active communications connection maintained with the first RAT.

Full Frequency Reuse in Mobile WiMAX and LTE Networks with Sectored Cells

Abstract: Frequency reuse is an important topic in wireless communications systems. In this paper, we address the issue of frequency reuse in sectored cells which are subject to interfer-ence in the overlap regions of adjacent sectors. We propose to increase the number of sectors from 3 to 4 using conventional base station sector antennas with beam-width exceeding 120°, which purposely creates large overlap regions between adjacent sectors. Rather than treating the signals of adjacent sectors as interference, we investigate sector cooperation for communica-tion with users located in the overlap regions. Different scenarios are considered for user locations, and simulation results are given which illustrate the performance of the proposed schemes.

An iterative channel estimator for fast-varying channels using successive OFDM symbols

Abstract: This paper deals with pilot-based channel estimation for fast varying channels in Orthogonal Frequency Division Multiplexing (OFDM) systems. Due to the variation of the channel during one OFDM symbol, one-tap channel estimation and the corresponding equalization is no longer the optimum solution and such a variation results in inter-carrier interference (ICI). One of the possible approaches to predict this interfering effect is to use basis expansion model (BEM) with which the variation of the channel can be approximated successfully. However, as the pure BEM does not solve completely the problem, we investigate the estimation problem using decision feedback to enhance the performance. In particular, we propose a simple algorithm based on using two successive OFDM symbols to filter channel coefficients and improve not only the convergence of pure decision feedback based estimation but also the system performance. Simulation results based on Jake's channel model with a high Doppler spread and a practical high data rate system sustain our claims.

Method and system for channel scanning in a wireless communications system

Abstract: A method is provided for channel scanning in a wireless communications system, for the identification of one or more narrow-band channels present in a certain frequency band and which can be used for connection between a wireless communications device and a communications network. The method includes: applying a FFT function to at least one signal corresponding to a given frequency band, providing for a set of coefficients each being representative of a frequency, analyzing the coefficients so as to detect at least one frequency region having at least one predetermined feature, and determining at least one channel position, by considering that each of the at least one frequency region having at least one predetermined feature is a guard band of one of the at least one channel.

Full Frequency Reuse in OFDMA-Based Wireless Networks with Sectored Cells

Abstract: Due to overlap of antenna radiation patterns and the resulting interference between sectors, different frequency bands are typically used in different sectors of a cell in cellular systems. In this paper, a full frequency reuse concept, which is based on multiple-input multiple-output (MIMO) techniques, is introduced and analyzed for the uplink and downlink. The results indicate a significant increase of the cell capacity.

Differential amplifier with common-mode feedback

Abstract: A fully differential amplifier comprises a first gain stage (11-13,15,16), a second gain stage (21,22), an active feedforward stage (23,24) and a common mode feedback stage (25,26,41-48). As shown in fig. 1 , the first gain stage (11-13,15,16) comprises a source-coupled pair of NMOS transistors (11,12) having their sources connected to a current source (13), while their drains are connected to a pair of load transistors (15,16). The amplified differential output signal is obtained across the output nodes (31,32) to which are coupled the outputs of the second gain stage (21,22) and the outputs of the active feedforward stage (23,24). As shown in fig. 3 , the common mode feedback stage comprises two differential amplifier stages (43,44 and 45,46), two diode-connected load transistors (41,42) and two feedforward transistors (31,32). Each one of the two differential amplifier stages receives a common reference voltage (Vref). The other input of each differential amplifier stage is connected to a respective output terminal (31,32) of the fully differential amplifier shown in fig. 1 . One of the diode-connected load transistors (41) is connected to the pair of load transistors (15,16) to form a current mirror, in order to control the common mode voltage at the amplifier outputs (31,32) via the load transistors (15,16) of the first gain stage. This diode-connected transistor (41) is simultaneously connected to the drains of a pair of feedforward transistors (25,26) providing a DC path between the source terminals of the active feedforward stage (23,24) and a reference potential (Vss).

MIMO techniques and full frequency reuse in mobile WiMAX systems

Abstract: We first review recent developments in multiple-input multiple-output (MIMO) techniques for mobile WiMAX systems and discuss full-rate and high-rate space-time codes of low decoder complexity. Next, we discuss the frequency reuse issue in sectored cells and point out the limitations due to overlapping of antenna radiation patterns of adjacent sectors and the resulting interference. Then, we discuss several frequency reuse concepts for the uplink and for the downlink. Some of these techniques are half rate, while others are full rate, both of them providing transmit diversity.

Scheduling-aided base station dynamic range extension

Abstract: The invention concerns an uplink wireless communication method between mobile stations (MS) and a base station (BS) configured to receive signals transmitted over a dynamic power range (DR), the method comprising the steps consisting of: - identifying at least one mobile station (MS#) authorized to transmit, - determining, for a given uplink frame (UL#), a total communication time (COM_TOT_UL#), - selecting at least one mobile station (MS#) authorized to transmit, and - allocating to each mobile station (MS#) authorized to transmit a respective communication time (COM_MS#_UL#) equal to or less than the total communication time (COM_TOT_UL#) of said uplink frame (UL#). According to the invention, it also comprises the steps consisting of: - determining a plurality of time periods (T1, T2, ..., Tn), and - for each said time period, applying a respective value of said dynamic range (DR) of said base station (BS).

Method for transmitting a sequence of symbols for exploiting transmit diversity

Abstract: An embodiment of a method for transmitting data through at least a channel in a wireless communication system, the method comprising at least the steps of: encoding the data by performing a forward-error-correction encoding, forming a sequence of symbols from the encoded data, forming an M-by-T coding matrix from said sequence of symbols, each column of the coding matrix comprising N different symbols of the sequence of symbols and M−N zeros, N being an integer equal at least to one, T representing the number of consecutive transmission intervals, M representing the total number of transmit antennas, and using the coding matrix for transmitting the sequence of symbols during the T consecutive transmission intervals, by transmitting one different column of the coding matrix at each transmission interval through the M transmit antennas, only N transmit antennas are enabled during a given transmission interval.

Method for estimating a received signal and corresponding device

Abstract: A method and apparatus for estimating a transmission channel in a receiver of an OFDMA signal formed by a plurality of carriers modulated by data elements and distributed in the time-frequency domain in successive symbols, the plurality of carriers including pilot carriers, modulated by reference data elements known by receivers The method includes: receiving a signal comprising a series of n symbols covering at least one resource block; making an initial channel estimation by identifying the pilot carriers included in the series of n symbols; determining diagonal entries of p frequency domain channel matrices G (x) for estimating the channel for at least x symbols among the n symbols, the x symbols being pilot symbols; determining, in the frequency domain, at least some non diagonal entries for each frequency domain channel matrix G of the n symbols from the determined diagonal entries of the x frequency domain channel matrices G (x)