Spread spectrum modulation and despreading demodulation method and device based on sequence cross-correlation characteristics
A technology of spread spectrum modulation and despreading, applied in electrical components, transmission systems, etc., can solve problems such as the reliability of power line carrier communication, achieve the effect of omitting the synchronization loop and reducing the implementation cost
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no. 1 example
[0050] In the actual application of this embodiment, according to the consideration of the data rate, the selection of the working clock and the implementation complexity and cost, etc., a pair of m-sequence optimal pairs with a length of 31 are selected as the spreading codewords, and the generator polynomials are respectively G a (x)=x 5 +x 2 +1 and G b (x)=x 5 +x 4 +x 3 +x 2 +1.
[0051] Taking the BPSK modulation method as an example, it specifically includes the following processing procedures:
[0052] figure 2 A structural block diagram of a communication system transmitter according to the first embodiment of the present invention is shown. refer to figure 2 As shown, the transmitter 200 includes a spreading unit 201 , a spreading code generator 202 , a baseband shaping filter 203 , a modulating unit 204 and a carrier generator 205 . The spreading unit 201, the baseband shaping filter 203 and the modulating unit 204 are connected in sequence. The spreading...
specific Embodiment approach
[0076] We noticed that the complete expressions of the two despread signals M(t) and N(t) of I and Q mentioned above contain two orthogonal factors of cos and sin respectively. When the carrier is fully synchronized, the correlation energy after despreading Concentrate on the I-way (in-phase branch); when the carrier is not synchronized, the energy will "leak" to the Q-way (orthogonal branch) to varying degrees. Therefore, through the squarers 309, 310 and the adder 311, the sum of the squares of M(t) and N(t) can be obtained to obtain a total correlation energy value independent of the carrier phase-frequency error:
[0077]
[0078] At the same time, according to the dual-code spread spectrum and single-code despreading strategies provided in this embodiment, there are:
[0079]
[0080] ready-to-use C a The sequence is simultaneously used as two local despreading code words of I and Q.
[0081] so at this time
[0082] where R a (k) is C a The autocorrelation f...
no. 2 example
[0086] Figure 4 A structural block diagram of a communication system receiver according to the second embodiment of the present invention is shown. refer to Figure 4 As shown, the receiver 400 of this embodiment includes demodulation units 401 and 403, local carrier generator 402, low-pass filters 404 and 405, despreading units 406 and 408, local despreading code generator 407, despreading unit 409 and 410 , an adder 411 , and a threshold decision unit 412 . The transmitter of this embodiment may be the same as the transmitter 200 of the first embodiment.
[0087] On the basis of the first embodiment, based on the consideration of reducing the cost of circuit implementation, when the receiver 400 of this embodiment calculates the total value of the relevant energy E(t), through the absolute value units 409, 410 and the adder 411, use The sum of absolute values operation approximates the sum of squares operation, namely:
[0088]
[0089] make It can be seen In a...
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