APPENDIX S. Space-Time Coding for Telemetry Systems

Transcription

1 APPENDIX S Space-Time Coding for Telemetry Systems Acronyms... S-iii 1.0 Code Description... S Modulation... S Resources... S-4 References... S-5 Tale of Figures Figure S-1. Offset QPSK IRIG 106 Symol-to-Phase Mapping Convention... S-1 Figure S-2. Notional Diagram Illustrating the Periodic Insertion of 128 Pilot Bits Every 3200 Alamouti-Encoded Bits... S-3 Figure S-3. A Notional Block Diagram of the Space-Time Code Transmitter... S-4

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3 Acronyms SOQPSK STC shaped offset quadrature phase shift keying space-time code S-iii

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5 1.0 Code Description APPENDIX S Space-Time Coding for Telemetry Systems The space-time code (STC) used in this standard is ased on the Alamouti STC 1 and applied only to shaped offset quadrature phase shift keying (SOQPSK)-TG or any of its fully interoperale variants. The Alamouti STC may e descried in terms of the offset QPSK IRIG 106 symol-to-phase mapping convention illustrated in Figure M-2 in Appendix M. Figure M-2 is reproduced here as Figure S-1. Figure S-1. Offset QPSK IRIG 106 Symol-to-Phase Mapping Convention The starting point is the normalized analog values corresponding to each of the offset QPSK symols. Let [an, n] with an = ±1, n = ±1 e the analog value of the n-th symol. Suppose the it sequence defines the sequence of symols [a0, 0], [a1, 1], [a2, 2], [a3, 3],, [a2k, 2k], [a2k+1, 2k+1], The Alamouti STC organizes the symols into locks of two symols, starting with the even-indexed locks as shown. The Alamouti STC assigns the k-th lock of symols [a2k, 2k], [a2k+1, 2k+1] to antenna 0 and antenna 1 over two consecutive symol times as shown elow. antenna symol time 2k symol time 2k+1 0 [a2k, 2k] [ a2k+1, 2k+1] 1 [a2k+1, 2k+1] [a2k, 2k] 1 S. Alamouti. A Simple Transmit diversity Technique for Wireless Communications. IEEE Journal on Selected Areas in Communications, vol. 16, no. 8, pp , Octoer S-1

6 Using the it (Boolean) assignments shown in Figure S-1, the Alamouti encoder can e restated in terms of the input its as follows. Let the sequence of input its e k 4k+1 4k+2 4k+3 The STC encoder groups the its into non-overlapping locks of four its each as indicated y the vertical lines. The STC encoder produces two it streams in parallel: 0, which is applied to antenna 0, and 1, which is applied to antenna 1. The relationship etween the input it sequence and these two it sequences is where n is the logical complement of it n k 4k 1 4k 2 4k 3 4k 2 4k 3 4k 4k 1 An important point here is the notion of even- and odd-indexed its. The SOQPSK-TG modulator treats even-indexed and odd-indexed its slightly differently. Each code lock must egin with an even-indexed it. An example of encoding is as follows. Suppose the input it sequence is The two STC encoded it sequences are = = To make provision for the estimation of frequency offset, differential timing, and the channels, a lock of known its, called pilot its, is periodically inserted into each of the two it streams. A 128-it pilot lock is inserted every 3200 Alamouti-encoded its. The pilot its inserted into 0 it stream are denoted p0 and the it pilot its inserted into the 1 it stream are denoted p1. These pilot it sequences are A notional diagram illustrating how p0 and p1 are periodically inserted into 0 and 1, respectively, is illustrated in Figure S-2. Note that the its comprising 0 and 1 may change with every occurrence as defined y the input data, ut the pilot its p0 and p1 do not change with each occurrence. S-2

7 Figure S-2. Notional Diagram Illustrating the Periodic Insertion of 128 Pilot Bits Every 3200 Alamouti-Encoded Bits 2.0 Modulation The it sequences descried in the previous section are modulated y a pair of SOQPSK- TG modulators (or modulator/transmitters). The modulators should e constructed and used as follows. The modulators share a common clock. This common clock is 26/25 times the input clock to accommodate the periodic insertion of 128 pilot its every 3200 Alamouti-encoded its. The modulators should share a common carrier reference. If this is not possile, the two carrier references should e phase-locked ideally, or frequency-locked at a minimum. Randomization, if required, should e applied efore the STC encoder. Differential encoding should e disaled. The periodically inserted pilot its are to e used y the demodulator to estimate the magnitudes and phases of the antenna-0-to-receiver channel and the antenna-1-to-receiver channel. There is no need to use differential encoding ecause data-aided phase estimates do not possess a phase amiguity. 2 Figure S-3 is a notional lock diagram that shows the relationship etween the input data and clock, the it-level space-time encoder, the periodic pilot it insertion, and the SOQPSK-TG modulation. 2 M. Rice. Digital Communications: A Discrete-Time Approach. Pearson/Prentice-Hall. Upper Saddle River, NJ, S-3

8 Figure S-3. A Notional Block Diagram of the Space-Time Code Transmitter 3.0 Resources Jensen, et al. 3 first descried the application of space-time coding to the two-antenna prolem. Experimental flights confirmed the effectiveness of the technique. 4,5,6 3 Jensen, M., M. Rice, and A. Anderson. Aeronautical Telemetry Using Multiple-Antenna Transmitters. IEEE Transactions on Aerospace and Electronic Systems, vol. 43, no. 1, pp , January M. Rice, Space-Time Coding for Aeronautical Telemetry: Part 1 System Description, in Proceedings of the International Telemetering Conference, Las Vegas, NV, Octoer Rice, M. and K. Temple, Space-Time Coding for Aeronautical Telemetry: part II Experimental Results, in Proceedings of the International Telemetering Conference, Las Vegas, NV, Octoer K. Temple, Performance Evaluation of Space-Time coding on an Airorne Test Platform, in Proceedings of the International Telemetering Conference, forthcoming. S-4

9 References Jensen, M., M. Rice, and A. Anderson. Aeronautical Telemetry Using Multiple-Antenna Transmitters. IEEE Transactions on Aerospace and Electronic Systems, vol. 43, no. 1, pp , January K. Temple. Performance Evaluation of Space-Time coding on an Airorne Test Platform, in Proceedings of the International Telemetering Conference, forthcoming. M. Rice. Digital Communications: A Discrete-Time Approach. Pearson/Prentice-Hall. Upper Saddle River, NJ, Space-Time Coding for Aeronautical Telemetry: Part 1 System Description, in Proceedings of the International Telemetering Conference, Las Vegas, NV, Octoer Rice, M. and K. Temple, Space-Time Coding for Aeronautical Telemetry: part II Experimental Results, in Proceedings of the International Telemetering Conference, Las Vegas, NV, Octoer S. Alamouti. A Simple Transmit Diversity Technique for Wireless Communications. IEEE Journal on Selected Areas in Communications, vol. 16, no. 8, pp , Octoer S-5

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