摘要:
A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method includes steps of, within a coverage area of a base station (BS), (a) assigning the same spreading code to a plurality of subscriber stations (SSs); and (b) beamforming using an antenna array at the BS so as to maximize the signal to interference plus noise ratio for a signal transmitted from a desired SS, The beamforming operates to steer a null towards another same-code SS to minimize interference from the same-code SS. Assuming that the antenna array has M-elements (M>1), then individual ones of P orthogonal spreading codes can be reused αM times within the coverage area, where 1/M
摘要:
A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method operates, within a coverage area of a base station (BS) or radio base unit (RBU) having a multi-element antenna array, for estimating a SSV for individual ones of a plurality of active subscriber stations (SSs) and assigns a spreading code to a subscriber station (SS) that minimizes the similarity of the determined SSVs of the SSs in a spreading code set. A metric used to measure the similarity of the spatial signature vectors of the SSs comprises the squared sum of the inner products of same code SSs' SSV with a current SS's SSV. The step of assigning includes calculating the magnitude of the squared inner product of the SSVs of all pairs of active SSs; using the calculated values for determining ξn(c) for each spreading code that is not already used some specified maximum number of times; and assigning to a SS the spreading code with a minimum ξn(c).
摘要:
A method is disclosed for operating a synchronous space division multiple access, code division multiple access communications system. The method operates, within a coverage area of a base station (BS) or radio base unit (RBU) having a multi-element antenna array, to assign spreading codes to users. The method estimates a spatial signature vector (SSV) for a current subscriber station; uses the estimated SSV as a weight vector when determining the output power that is correlated with each of a plurality of spreading code sequences and assigns a spreading code to the current subscriber station that is determined to have the minimum output power. The step of determining the output power includes steering a beamformer toward the current subscriber station by setting the weight vector equal to the SSV, and also determines the average squared value of the antenna array output that has been despread using a code i. The multi-element antenna array has M elements, and the step of determining the output power operates an M-branch receiver to despread a signal received on each element with a spreading code i, to accumulate the despread signal over a symbol duration, to scale the accumulated signal by the weight vector, to sum all of the scaled values and to square the result, and to average the squared result over R samples to determine the output power for code i for the current subscriber station. R may have a value in the range of about 16 symbols to about 64 symbols, and may be fixed or variable.
摘要:
The present invention concerns methods and apparatus for use in a spread spectrum communications system. In particular, in a method of the present invention information useful for acquiring a target signal is selected; the information is incorporated in an acquisition signal; the acquisition signal is transmitted; the target signal is spread with a spreading code; and the target signal is transmitted. At a receiving node, the acquisition information useful for acquiring the target signal is recovered from the acquisition signal and used to acquire the target signal. Apparatus in accordance with the present invention implement methods of the present invention. The methods and apparatus of the present invention can be used in node- and network-discovery situations.
摘要:
A first node initiating communications with a second node already in a secure network sends a discovery burst having a preamble portion and a payload portion. The preamble portion is sent at a varying frequency between high and low thresholds that are reflective of Doppler uncertainty between the nodes. The second node continuously listens at a frequency, termed an acquisition frequency. A data sequence in the preamble portion, known to the second node, is received and used to determine the receive instant in the preamble portion, and thereby compare against the known frequency ramp to determine the frequency at which the payload portion will be received. Preferably, the first node varies the preamble portion between thresholds more than once within the time span of a single preamble portion, and the preamble and payload portions are spread with different spreading codes. The preamble portion may also be disguised with noise generated by the first node.
摘要:
A matched filter decorrelator is described for efficiently performing a carrier frequency search while despreading a P/N long code constructed from two or more constituent codes such as codes A, B, C. The received signal is phase rotated into a frequency bin and partially despread, preferably over all but one of the constituent codes. To despread the final constituent code, the partially despread signal is input in parallel into frequency bins, where a phase rotator sets each input to a different bin. The frequency bins are then despread in parallel over the final constituent code, and an energy peak in one accumulator indicates which bin is the carrier frequency. Alternatively, a Fourier transform could be used over each of the frequency bins. By partially despreading prior to division into carrier frequency bins, hardware and computational burden are reduced as compared to prior art decorrelators. The present invention is particularly apt for use with an acquisition burst in a secure network.
摘要:
Disclosed is a method for operating a code division multiple access communications system, and a system that operates in accordance with the method. The method operates within a coverage area of a base station by assigning a set of spreading codes to individual ones of a plurality of subscriber stations and then, during transmissions within the cell, by periodically hopping amongst spreading code within the set of spreading codes such that at any given time no two subscriber stations operate with the same spreading code. The set of spreading codes may include the all one's spreading code. The step of periodically hopping preferably changes from a currently used spreading code to a next spreading code at a symbol rate or at a multiple of the symbol rate. The set of spreading codes may be a hopped sub-set of a larger set of spreading codes, and in this case the method further operates to assign a non-hopped sub-set of the larger set of spreading codes to individual ones of the plurality of subscriber stations for use on a system access channel and/or on a system control channel or, more generally, for use on a non-traffic channel. The system may be a fixed data rate system or a variable data rate system. In the latter case the step of periodically hopping may change from a currently used spreading code to a next spreading code at the symbol rate, or at a multiple of the symbol rate of the lowest or the highest symbol rate users.
摘要:
A method is disclosed for operating a wireless communications system, such as a DS-CDMA communications system, by transmitting a waveform that includes a plurality of repeating frames each having x header training base symbols in a header training symbol field (TH) and y tail training base symbols in a tail training symbol field (TT). The frame is received and functions as one of a plurality of different types of frames depending on the content of at least TT. In the preferred embodiment the frame functions as one of a normal traffic frame, a termination frame, or a legacy frame providing backwards compatibility with another waveform. A given one of the frames includes four equal-size data fields separated by three equal-sized control fields, the header training symbol field (TH) and the tail training symbol field (TT).
摘要:
A first node seeking entry into a secure spread spectrum communications network sends a discovery burst at a low rate, and sends traffic bursts at a higher rate to exchange data rate for range. A receiving node receives discovery bursts via an omni-directional link and transmits and receives traffic bursts via directional links. As a node within the network detects a fading signal, it transmits a discovery burst at low rate on both its uplink and downlink channels. Other nodes may reply via the original uplink channel, and the fading node updates a list of candidate nodes through which it can relay through the network to its intended recipient by reversing the link direction of its original uplink and original downlink channels.
摘要:
A method for constructing and selecting non-recursive orthogonal variable spreading factor (OVSF) codes is provided. The method includes: defining a variable B=SFmax/SFmin, where SFmax is a maximum desired spreading factor and SFmin is a minimum desired spreading factor; forming B unique base matrices Gk of dimension SFmin×SFmin, where GiGiT=SFminImin ∀i, where T denotes a matrix transpose and Imin is an SFmin×SFmin identity matrix; forming a modulation matrix M of dimension B×B such that MMT=BIB, where IB is a B×B identity matrix; forming an SFmax×SFmax orthogonal variable spread factor (OVSF) code matrix C′ as: C ′ = [ M 1 , 1 · G 1 M 1 , 2 · G 2 … M 1 , B · G B M 2 , 1 · G 1 M 2 , 2 · G 2 … M 2 , B · G B ⋮ ⋮ ⋰ ⋮ M B , 1 · G 1 M B , 2 · G 2 … M B , B · G B ] , where Mi,j is a scalar from the i-th row and j-th column of the modulation matrix M, Gl . . . GB is the k-th base matrix Gk and Mi,j·Gk denotes the multiplication of the elements of Gk by the scalar Mi,j; selecting a row of the OVSF code matrix C′ to use as a pseudo-noise (PN) code; and one of spreading or despreading a signal using the selected PN code.
摘要翻译:提供了一种用于构造和选择非递归正交可变扩展因子(OVSF)码的方法。 该方法包括:定义变量B = SFmax / SFmin,其中SFmax是最大期望扩频因子,SFmin是最小期望扩频因子; 形成尺寸为SFminxSFmin的B唯一基本矩阵Gk,其中GiGiT = SFminImin∀i,其中T表示矩阵转置,Imin是SFminxSFmin单位矩阵; 形成尺寸为BxB的调制矩阵M,使得MMT = BIB,其中IB是BxB单位矩阵; 形成SFmaxxSFmax正交可变扩展因子(OVSF)码矩阵C'为:C'= [M 1, G 1 M 1,2, G 2 ... M 1,B。 G B M 2,1。 G 1 M 2,2。 G 2 ... M 2,B。 B,⋮⋮⋰⋮M B,1。 G 1 M B,2。 G 2 ... M B,B。 G B],其中Mi,j是从调制矩阵M,G1的第i行和第j列的标量。 。 。 GB是第k个基本矩阵Gk和Mi,j.Gk表示Gk的元素乘以标量Mi,j; 选择一行OVSF码矩阵C'以用作伪噪声(PN)码; 以及使用所选PN码扩展或解扩信号的一个。