Unified synchronous ranging channel structure and ranging code generation and detection in wireless OFDMA systems
A unified synchronous ranging channel is provided. The unified synchronous ranging channel has a ranging cyclic prefix length that is the same as a cyclic prefix length of a data channel. The unified synchronous ranging channel is used for one of initial ranging, handover ranging, and periodic ranging between a mobile station and a femto base station. In one embodiment, the synchronous ranging channel spans over a two-dimensional radio resource region having a first number of subcarriers along frequency domain, a second number of OFDM symbols along time domain, and a third number of time-domain repetition. At the transmit side, a ranging code sequence is generated by applying a fixed time-domain cyclic shift per OFDM symbol to a root sequence. At the receive side, the ranging code sequence is decoded by using a summation module, a likelihood-combining module, and a modified peak test module that normalizes a peak value.
1. A method of uplink synchronization in a cellular OFDMA system, the method comprises:
mapping a ranging code onto a synchronous ranging channel by a mobile station, wherein the synchronous ranging channel has a ranging cyclic prefix (RCP) length that is the same as a cyclic prefix (CP) length of a data channel; and
transmitting the synchronous ranging channel to a femto base station, wherein the synchronous ranging channel spans over a two-dimensional radio resource region having a first number of subcarriers along frequency domain, a second number of OFDM symbol along time domain, and a third number of time-domain repetition.
2. The method of claim 1 , wherein the ranging code has a code sequence that is mapped onto the synchronous ranging channel for transmission, and wherein the code sequence is optionally repeated along the time domain.
3. The method of claim 2 , wherein the synchronous ranging channel is further frequency division multiplexed (FDM) with data channels in a scheduling interval.
4. The method of claim 2 , wherein the synchronous ranging channel is further time division multiplexed (TDM) with data channels in a scheduling interval.
5. The method of claim 1 , wherein the synchronous ranging channel is further time division multiplexed (TDM) with a plurality of synchronous ranging channels in a scheduling interval.
6. The method of claim 5 , wherein the synchronous ranging channel and the plurality of synchronous ranging channels are utilized by the same femto base station and code division multiplexed (CDM) among different base stations in a scheduling interval.
7. The method of claim 5 , wherein the synchronous ranging channel and the other multiple synchronous ranging channels are utilized by different base stations and TDM/CDM among the different base stations in a scheduling interval.
8. The method of claim 7 , wherein the TDM/CDM mechanism is determined by configuration information transmitted via a broadcast channel.
9. The method of claim 8 , wherein the broadcast channel contains Super Frame Header (SFH).
10. The method of claim 1 , wherein the ranging code and a ranging message are both mapped onto the ranging channel to be transmitted together by the mobile station.
11. The method of claim 10 , wherein the ranging message contains at least one of a mobile station ID and bandwidth requirement information for uplink access.
12. The method of claim 1 , wherein the synchronous ranging channel is used for one of an initial ranging, a handover ranging, a periodic ranging, and a bandwidth request ranging.
13. A method, comprising:
generating a cyclic ranging code sequence by a mobile station in an OFDMA system, wherein the cyclic ranging code is mapped onto a ranging channel that spans over a first number of subcarriers along frequency domain, a second number of Orthogonal Frequency Division Multiplexing (OFDM) symbols along time domain, and a third number of time-domain repetition, and wherein the cyclic ranging code sequence is generated by applying a fixed time-domain cyclic shift per OFDM symbol to a root sequence selected from a plurality of root sequences; and
transmitting the cyclic code sequence using the ranging channel, wherein the cyclic code sequence is detected at a receiver side by frequency domain correlation that involves only the plurality of root sequences.
14. The method of claim 13 , wherein the plurality of root sequences is a set of Zadoff-Chu sequences.
15. The method of claim 13 , wherein the fixed time-domain cyclic shift in each of the second number of Orthogonal Frequency Division Multiplexing (OFDM) symbols is determined based on a subcarrier index of the ranging channel along frequency domain.
16. The method of claim 13 , wherein the ranging channel is used for one of an initial ranging, a handover ranging, a periodic ranging, and a bandwidth request ranging between the mobile station and a femto base station.
17. A base station, comprising:
a receiver that receives a ranging code sequence, wherein the ranging code sequence is transmitted via a synchronous ranging channel that spans over a radio resource region having a first number of subcarriers along frequency domain, a second number of Orthogonal Frequency Division Multiplexing (OFDM) symbol along time domain, and a third number of time-domain repetition, and wherein the ranging code sequence is partitioned into a second number of code portions and each code portion is allocated in a corresponding OFDM symbol; and
a decoder that decodes the ranging code sequence from a plurality of codes having a corresponding code index, the decoder comprising:
a summation module that sums a second number of correlated vectors of each code portion for each code index and outputs a summed vector for each code index; and
a peak test module that detects a peak value based on the summed vector for each code index, normalizes each peak value, and compares each normalized peak value with a corresponding threshold value such that a possible code index is detected.
18. The base station of claim 17 , wherein the summation module sums the correlated vectors in time domain after IFFT processing.
19. The base station of claim 17 , wherein the summation module sums the correlated vectors in frequency domain before IFFT processing.
20. The base station of claim 17 , wherein the ranging code sequence is repeated for the third number of times along time domain, wherein the decoder comprises a corresponding summation module for each repetition, and wherein each repetition is decoded independently and then summed by the corresponding summation modules.
21. The base station of claim 20 , wherein the decoder further comprises a likelihood-combining module that outputs combined likelihood vectors based on outputs of the corresponding summation modules.
22. The base station of claim 17 , wherein the base station is a femto base station, and wherein the synchronous ranging channel is used for one of an initial ranging, a handover ranging, a periodic ranging, and a bandwidth request ranging.