NLOS WIRELESS BACKHAUL DOWNLINK COMMUNICATION

• US 20140362701A1
• Filed: 06/05/2014
• Published: 12/11/2014
• Est. Priority Date: 06/05/2013
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: ROH, June Chul, BERTRAND, Pierre, HOSUR, Srinath, POTHUKUCHI, Vijay, MANSOUR, Mohamed Farouk
• Granted Patent: US 10,334,569 B2
• Time in Patent Office: Days
• US Class Current: 370/235
• CPC Class Codes: H03M 13/1515 Reed-Solomon codes
• CPC Class Codes: H03M 13/2966 Turbo codes concatenated with another code, e.g. an outer block code
• CPC Class Codes: H03M 13/611 Specific encoding aspects, e.g. encoding by means of decoding
• CPC Class Codes: H03M 13/618 Shortening and extension of codes
• CPC Class Codes: H03M 13/635 Error control coding in combination with rate matching
• CPC Class Codes: H04H 20/38 Arrangements for distribution where lower stations, e.g. receivers, interact with the broadcast
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0061 Error detection codes
• CPC Class Codes: H04L 1/0064 Concatenated codes
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 1/0076 Distributed coding, e.g. network coding, involving channel coding coding in both space and time H04L1/0618; cooperative diversity H04B7/022
• CPC Class Codes: H04L 1/1812 Hybrid protocols; Hybrid automatic repeat request [HARQ]
• CPC Class Codes: H04W 72/0446 Resources in time domain, e.g. slots or frames
• CPC Class Codes: H04W 72/21 in the uplink direction of a wireless link, i.e. towards the network

Abstract

A method for communicating over a wireless backhaul channel comprising generating a radio frame comprising a plurality of time slots, wherein each time slot comprises a plurality of symbols in time and a plurality of sub-carriers in a system bandwidth, broadcasting a broadcast channel signal comprising a transmission schedule to a plurality of remote units in a number of consecutive sub-carriers centered about a direct current (DC) sub-carrier in at least one of the time slots in the radio frame regardless of the system bandwidth, and transmitting a downlink (DL) control channel signal and a DL data channel signal to a first of the remote units, wherein the DL data channel signal is transmitted by employing a single carrier block transmission scheme comprising a Discrete Fourier Transform (DFT) spreading for frequency diversity.

Claims

1. A method for communicating over a wireless backhaul channel, comprising:

generating a radio frame comprising a plurality of time slots, wherein each time slot comprises a plurality of symbols in time and a plurality of sub-carriers in a system bandwidth, and wherein the radio frame comprises an adjustable link directionality ratio of a number of the time slots for an uplink (UL) direction and the number of time slots for a downlink (DL) direction to provide traffic load balancing;

broadcasting a broadcast channel signal to a plurality of remote units in a number of consecutive sub-carriers centered about a direct current (DC) sub-carrier in at least one of the time slots in the radio frame regardless of the system bandwidth, wherein the broadcast channel signal comprises a transmission schedule comprising slot assignments that indicate a link direction and a transmission opportunity for a first of the plurality of remote units; and

transmitting a DL control channel signal and a DL data channel signal to the first remote unit, wherein the DL control channel signal comprises DL control information that controls transmission of the DL data channel signal,

wherein the broadcast channel signal, the DL control channel signal, and the DL data channel signal are transmitted by employing a time-frequency multiplex scheme, and

wherein the DL data channel signal is transmitted by employing a single carrier block transmission scheme comprising a Discrete Fourier Transform (DFT) spreading for frequency diversity.

2. The method of claim 1, wherein each time slot comprises a fixed time duration, and wherein the transmission schedule comprises a scheduling period about a half radio frame time duration or a full radio frame time duration.

3. The method of claim 2, wherein the fixed time duration comprises about 0.5 milliseconds (ms) to provide low transmission latency, and wherein the radio frame comprises about twenty time slots.

4. The method of claim 1 further comprising transmitting a pilot sequence (PS) in a symbol time spanning all the sub-carriers in the system bandwidth, wherein the PS comprises a pre-determined sequence comprising signal properties that provide channel estimation capabilities in the system bandwidth.

5. The method of claim 4, wherein the PS is transmitted at a beginning of each time slot assigned for the DL direction to provide low receive processing latency at the remote units.

6. The method of claim 4, wherein the PS is transmitted at about a middle of each time slot assigned for the DL direction to provide channel estimation with low timing drift in a time-varying channel.

7. The method of claim 1, wherein the radio frame comprises at least one specific time slot comprising a DL time period, a guard time period to provide a link direction switching opportunity, and an UL time period to provide an UL random access opportunity, and wherein the broadcast channel signal is broadcasted in the DL time period of the specific time slot.

8. The method of claim 7, wherein the DL time period comprises about four symbols, wherein the guard time period comprises about one symbol, and wherein the UL time period comprises about two symbols.

9. The method of claim 7, wherein the specific time slot is located at about a third time slot in the radio frame, at about a thirteenth time slot in the radio frame, or combinations thereof.

10. The method of claim 7 further comprising transmitting a synchronization sequence (SS) in a same set of sub-carriers as the broadcast channel signal in the DL time period of the specific time slot by time multiplexing with the broadcast channel signal, wherein the SS comprises a pre-determined sequence comprising signal properties that provide signal detection capabilities for identifying the radio frame.

11. The method of claim 10, wherein the SS sequence is transmitted in about one symbol time, and wherein the broadcast channel signal is transmitted in about two symbol time.

12. The method of claim 1, wherein the broadcast channel signal and the DL control channel signal are transmitted by employing the single carrier block transmission scheme.

13. The method of claim 1, wherein the DL control channel signal is transmitted in a first set of the sub-carriers located near a higher frequency edge of the system bandwidth and a second set of the sub-carriers located near a lower frequency edge of the system bandwidth.

14. The method of claim 1, wherein the slot assignments comprise a slot assignment for the first remote unit for UL transmission, wherein the DL control channel signal further comprises UL control information for the UL transmission, and wherein the method further comprises:

combining at least some of the DL control information and at least some of the UL control information to generate a control frame; and

computing a Cyclic Redundancy Check (CRC) for the control frame.

15. The method of claim 1 further comprising:

receiving a UL data channel signal comprising a UL data frame from the first remote unit;

generating a hybrid automatic repeat request (HARQ) feedback signal according to a reception status of the UL data frame;

mapping the HARQ feedback signal to a first set of the sub-carriers located near a higher frequency edge of the system bandwidth; and

repeating the mapping of the HARQ feedback signal to a second set of the sub-carriers located near a lower frequency edge of the system bandwidth.

16. An apparatus, comprising:

a processing resource configured to;

perform single carrier modulation on a plurality of data bit streams to generate a plurality of Single Carrier-Frequency Division Multiple Access (SC-FDMA) frames, wherein to perform the single carrier modulation on each data bit stream, the processing resource is to;

perform symbol mapping on each data bit stream to generate a plurality of modulated data symbols; and

perform Discrete Fourier Transform (DFT) precoding on the modulated data symbols; and

perform frequency-time multiplexing to combine at least one of the SC-FDMA frames with an Orthogonal Frequency Division Multiplexing (OFDM) frame to generate a digital radio frame; and

a radio front end interface coupled to the processing resource and configured to cause the digital radio frame to be transmitted to a wireless backhaul remote unit.

17. The apparatus of claim 16, wherein the data bit streams comprise a broadcast channel data bit stream and a downlink (DL) control channel bit stream, wherein the broadcast channel bit stream is symbol mapped according to a first fixed modulation coding scheme (MCS), and wherein the DL control channel bit stream is symbol mapped according to a second fixed MCS.

18. The apparatus of claim 16, wherein the data bit streams comprise a broadcast channel bit stream comprising a transmission schedule, and wherein the processing resource is further configured to map the broadcast channel bit stream onto a fixed set of frequency sub-carriers centered about a direct current (DC) sub-carrier regardless of a system bandwidth.

19. The apparatus of claim 16, wherein the data bit streams comprise a downlink (DL) transmission control channel bit stream comprising a modulation coding scheme (MCS), and wherein the processing resource is further configured to map the DL transmission control channel bit stream onto a first set of frequency sub-carriers located near a higher frequency edge of a system bandwidth and a second set of the frequency sub-carriers located near a lower frequency edge of the system bandwidth to provide frequency diversity.

20. The apparatus of claim 16, wherein the OFDM frame comprises a hybrid automatic repeat request (HARQ) indicator frame, wherein the radio front end interface is further configured to receive an uplink (UL) digital radio frame comprising a UL data frame, wherein the processing resource is further configured to generate the HARQ frame to provide a reception status associated with the UL data frame, wherein the HARQ indicator frame comprises a plurality of frequency domain symbols, and wherein to perform the frequency-time multiplexing, the processing resource is further configured to:

map the frequency domain symbols onto a first set of frequency sub-carriers located near a higher frequency edge of a system bandwidth; and

repeat the mapping of the frequency domain symbols onto a second set of the frequency sub-carriers located near a lower frequency edge of the system bandwidth to provide frequency diversity.

21. The apparatus of claim 16, wherein the data bit streams comprise a broadcast channel data bit stream and a downlink (DL) control channel bit stream, and wherein the processing resource is further configured to perform an Alamouti type space-frequency block coding (SFBC) on the broadcast channel bit stream and the DL control channel bit stream to provide transmit diversity.

22. The apparatus of claim 16, wherein the digital radio frame comprises a plurality of SC-FDMA symbols in time, and wherein the processing resource is further configured to map a non-time varying pilot sequence (PS) onto all frequency sub-carriers in a system bandwidth in a SC-FDMA symbol time in the digital radio frame, and wherein the PS provides channel estimation capabilities in the system bandwidth.

23. The apparatus of claim 16, wherein the data bit streams comprise a downlink (DL) shared channel data bit stream associated with the wireless backhaul remote unit, and wherein the processing resource is further configured to:

perform Reed Solomon (RS) encoding on the DL shared channel data bit stream to generate a plurality of RS codewords;

perform byte interleaving across the RS codewords to generate an interleaved frame;

segment the interleaved frame into a plurality interleaved sub-frames; and

perform Turbo encoding on each interleaved sub-frame to generate a Turbo codeword.

24. The apparatus of claim 16, wherein the data bit streams comprise a broadcast channel data bit stream and a downlink (DL) control channel bit stream, and wherein the processing resource is further configured to perform tail-biting convolutional code on the broadcast channel bit stream and the DL control channel bit stream.

25. The apparatus of claim 24, wherein the processing resource is further configured to perform Reed Solomon (RS) encoding on the broadcast channel bit stream and the DL control channel bit stream prior to performing the tail-biting convolutional code.

26. The apparatus of claim 24, wherein the processing resource is further configured to perform rate matching and scrambling on the broadcast channel bit stream and the DL control channel bit stream.

27. The apparatus of claim 16, wherein the processing resource is further configured to map a synchronization sequence (SS) onto a fixed set of frequency sub-carriers centered about a direct current (DC) sub-carrier regardless of a system bandwidth, and wherein the SS sequence comprises a random Constant Amplitude Zero Auto-Correlation (CAZAC) sequence to provide signal detection capabilities against a carrier frequency offset.

28. The apparatus of claim 16, wherein the digital radio frame comprises a plurality of SC-FDMA symbols in time, and wherein the processing resource is further configured to perform a half sub-carrier frequency shifting on the SC-FDMA symbols without a phase reset for each SC-FDMA symbol.

29. A wireless backhaul communication system, comprising:

a transmitter comprising;

a Reed Solomon (RS) encoder configured to perform RS encoding on a downlink (DL) data bit stream to generate a plurality of RS codewords;

a byte interleaver coupled to the RS encoder and configured to perform byte interleaving across the plurality of RS codewords;

a Turbo encoder coupled to the byte interleaver and configured to perform Turbo encoding on the interleaved RS codewords to generate one or more Turbo codewords, wherein each Turbo codeword is encoded from multiple RS codewords;

a symbol mapper coupled to the Turbo encoder and configured to modulate and Discrete Fourier Transform (DFT) precode the Turbo codewords, a transmission control frame, and a broadcast frame separately, wherein the broadcast frame comprises a transmission schedule for a plurality of wireless backhaul remote units; and

a sub-carrier mapper coupled to the symbol mapper and configured to generate a first digital radio frame comprising a plurality of symbols in time and a plurality of sub-carriers in a system bandwidth, wherein to generate the first digital radio frame, the sub-carrier mapper is to;

map the DFT precoded broadcast frame onto a first set of the sub-carriers centered about a direct current (DC) sub-carrier, wherein the first set of sub-carriers comprises a fixed number of consecutive sub-carriers regardless of the system bandwidth;

map the DFT precoded transmission control frame onto a second set of the sub-carriers near a lower frequency edge and near a higher frequency edge of the system bandwidth; and

map the DFT precoded Turbo codewords onto frequency sub-carriers different than the first set of sub-carriers and the second set of sub-carriers; and

a radio front end comprising an antenna and coupled to the transmitter, wherein the radio front end is configured to convert the first digital radio frame to a first analog signal and transmit the first analog signal via the antenna.

30. The system of claim 29, wherein the transmitter further comprises a pilot sequence (PS) generator configured to generate a PS sequence and time multiplex the PS sequence with the DFT precoded broadcast frame, the DFT precoded transmission control frame, and the DFT precoded Turbo codewords, wherein the sub-carrier mapper is further configured to map the PS sequence onto all sub-carriers in the system bandwidth, and wherein the PS sequence provides channel estimation capabilities in the system bandwidth.

31. The system of claim 29, wherein the transmitter further comprises a synchronization sequence (SS) generator configured to generate a SS sequence and time multiplex the SS sequence with the DFT precoded broadcast frame, the DFT precoded transmission control frame, and the DFT precoded Turbo codewords, wherein the sub-carrier mapper is further configured to map the SS sequence onto a set of sub-carriers spanning a same frequency band as the first set of sub-carriers, and wherein the SS sequence comprises a random Constant Amplitude Zero Auto-Correlation (CAZAC) sequence to provide signal detection capabilities against a carrier frequency offset.