Methods and apparatus using cell-specific and common pilot subcarriers in multi-carrier, multi-cell wireless communication networks

• US 8,009,660 B2
• Filed: 01/20/2005
• Issued: 08/30/2011
• Est. Priority Date: 01/29/2004
• Status: Active Grant

• Current Assignee: Neo Wireless LLC (f/k/a CFIP NCF LLC) (SoftBank Group Corp.)
• Original Assignee: Neocific Incorporated
• Inventors: Lo, Titus, Huang, Haiming, Li, Xiaodong, Li, Kemin
• Primary Examiner(s): Afshar; Kamran
• Assistant Examiner(s): Sarwar; Babar
• Application Number:
  US10/583,530
• Publication Number:
  US 20070230388A1
• Time in Patent Office: 2,413 Days
• Field of Search: 455 6711- 6713, 455/115.1, 455/423, 455436-444, 455/502, 370331-332, 370/324, 370/350
• US Class Current: 370/350
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04J 11/005 of intercell interference
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/2637 with direct modulation of individual subcarriers
• CPC Class Codes: H04L 27/2646 using feedback from receiver for adjusting OFDM transmission parameters, e.g. transmission timing or guard interval length
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0016 Time-frequency-code
• CPC Class Codes: H04L 5/0028 Variable division signaling therefor H04L5/0092
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04W 16/02 Resource partitioning among network components, e.g. reuse partitioning
• CPC Class Codes: H04W 72/044 : based on the type of the allocated resource
• CPC Class Codes: H04W 72/0446 : Resources in time domain, e.g. slots or frames

Abstract

A multi-carrier cellular wireless network (400) employs base stations (404) that transmit two different groups of pilot subcarriers: (1) cell-specific pilot subcarriers, which are used by a receiver to extract information unique to each individual cell (402), and (2) common pilots subcarriers, which are designed to possess a set of characteristics common to all the base stations (404) of the system. The design criteria and transmission formats of the cell-specific and common pilot subcarriers are specified to enable a receiver to perform different system functions. The methods and processes can be extended to other systems, such as those with multiple antennas in an individual sector and those where some subcarriers bear common network/system information.

Claims

1. A multi-carrier, multi-cell, wireless communication network, comprising:

a plurality of base stations, each base station associated with one of a plurality of cells, having a transmitter that is synchronized in time and frequency with transmitters in other base stations in the plurality of cells, and configured to transmit cell-specific pilot subcarriers, cell-specific data subcarriers, common pilot subcarriers, and common data subcarriers within a same frequency band that is divided into a plurality of subcarriers, wherein;

the cell-specific pilot subcarriers and the cell-specific data subcarriers contain information concerning a specific cell, wherein at least some of the cell-specific pilot subcarriers are not aligned in frequency subcarrier index with cell-specific pilot subcarriers transmitted by the other base stations and at least some of the cell-specific data subcarriers are not aligned in frequency subcarrier index with cell-specific data subcarriers transmitted by the other base stations;

the common pilot subcarriers and the common data subcarriers contain information common to the plurality of cells, wherein the common pilot subcarriers are aligned in frequency subcarrier index with common pilot subcarriers transmitted by the other base stations and the common data subcarriers are aligned in frequency subcarrier index with common data subcarriers transmitted by the other base stations; and

a mobile station in one of the plurality of cells, the mobile station configured to receive the cell-specific pilot subcarriers and the cell-specific data subcarriers corresponding to the cell, and the common pilot subcarriers and the common data subcarriers corresponding to the plurality of cells, and, wherein the mobile station is further configured to;

determine cell-specific channel coefficients based on received signals on the cell-specific pilot subcarriers and apply the cell-specific channel coefficients to received signals on the cell-specific data subcarriers to compensate for cell-specific channel effects and to recover cell-specific information carried on the cell-specific data subcarriers, wherein the cell-specific channel corresponds to the channel from the base station in the cell to the mobile station; and

determine composite channel coefficients based on received signals on the common pilot subcarriers and apply the composite channel coefficients to received signals on the common data subcarriers to compensate for composite channel effects and to recover common information carried on the common data subcarriers, wherein the composite channel corresponds to an aggregate of different channels from the plurality of base stations to the mobile station.

2. The network of claim 1, wherein the common pilot subcarriers transmitted by different base stations are identical.

3. The network of claim 1, wherein the mobile station estimates a frequency of a received signal by 2π

f,Δ

t=arg{s_i*(k)s_i(k+1)}−

β

_i, using common pilot subcarriers of a same frequency index i at different times t_k and t_k+1, provided that;

AΔ

t<

<

a coherence period of a communication channel;

α

_i,m(t_k)=c_iα

_i,m(t_k+1); and

φ

_i,m(t_k)=φ

_8,m(t_k+1)+β

_i,

where;

4. The network of claim 1, wherein the mobile station computes a sampling period T_s(t_k) at the time t_k of a received signal by 2π

Δ

fT_s(t_k)=arg {s_i*(t_k)s_n(t_k)}−

γ

(t_k), using two common pilot subcarriers, transmitted at the same time t_k but of different frequency indices i and n, provided that;

Δ

f<

<

a coherence bandwidth of a communication channel;

α

_i,m(t_k)=c(t_k)α

_n,m(t_k); and

φ

_i,m(t_k)=φ

_n,m(t_k)+γ

(t_k),

where;

5. The network of claim 1, wherein phase diversity is achieved by the base station adding a random phase (_l,m) to a i^th subcarrier such that:

φ

_l,m(t_k)=φ

_i,m(t_k)+_l,m and φ

_l,m(t_k+1)=φ

_i,m(t_k+1)+_l,m,

where;

_l,m is different for each cell;

φ

_l,m(t_k)=φ

_i,m+β

_l, for all values of m;

−

π

≦

β

_i≦

β

π

is a predetermined constant for the plurality of cells; and

φ

_i,m(t_k) denotes phase at time t_k, associated with an i^th subcarrier from the base station of the m^th cell.

6. The network of claim 1, wherein the base station is configured to apply power control to the pilot subcarriers by adjusting the power of the pilot subcarriers individually or in subgroups comprising a plurality of pilot subcarriers.

7. The network of claim 1, wherein each of the plurality of base stations include multiple antennas within an individual sector and employ multiple transmission branches connected to different antennas, and wherein for frequency estimation the common pilot subcarriers for each transmission branch are generated such that:

α

_i,m(t_k)=c_ia_i(t_k+1) and φ

_i,m(t_k)=φ

_i,m(t_k+1)+β

_i,

where;

c_i>

0 and −

π

≦

β

_i≦

π

are predetermined constants for the plurality of cells; and

α

_i,m(t_k) and φ

_i,m(t_k) denote signal amplitude and phase at time t_k, associated with an i^th subcarrier from a base station of the m^th cell.

8. The network of claim 1, wherein each of the plurality of base stations include multiple antennas within an individual sector and employ multiple transmission branches connected to different antennas, and wherein for timing estimation the common pilot subcarriers for each transmission branch are generated such that:

a_i,m(t_k)=c(t_k)α

_n,m(t_k) and φ

_i,m(t_k)=φ

_n,m(t_k)+γ

(t_k),

where;

c(t_k)>

0 and −

π

≦

γ

(t_k)≦

π

are predetermined constants for the plurality of cells; and

α

_i,m(t_k) and φ

_i,m(t_k) denote signal amplitude and phase at time t_k, associated with an i^th subcarrier from a base station of the m^th cell.

9. The network of claim 1, wherein both the cell-specific pilot subcarriers and the common pilot subcarriers are used for frame synchronization, frequency offset estimation, or timing estimation.

10. The network of claim 1, wherein a microprocessor computes attributes of the pilot subcarriers, specified by their requirements, and inserts them in between data subcarriers contained in an electronic memory.

11. A method of generating transmission subcarriers in a base station in a multi-carrier, multi-cell, wireless communication system comprised of a plurality of mobile stations and base stations in a plurality of cells, the base station associated with a cell in the plurality of cells, including a transmitter that is synchronized in time and frequency with transmitters in other base stations in the system, and configured for generating different types of subcarriers within a same frequency band that is divided into a plurality of subcarriers, the method comprising:

generating common data subcarriers that carry data common to the plurality of cells to mobile stations in the plurality of cells;

generating common pilot subcarriers that possess characteristics common to other common pilot subcarriers generated by the other base stations in the system, the common pilot subcarriers enabling a mobile station in the cell to determine composite channel coefficients and apply the composite channel coefficients to signals on the common data subcarriers received by the mobile station to compensate for composite channel effects and to recover common data carried by the common data subcarriers, wherein the composite channel corresponds to an aggregate of different channels from the plurality of base stations to the mobile station;

generating cell-specific data subcarriers that carry data specific to the cell associated with the base station to individual mobile stations within the cell; and

generating cell-specific pilot subcarriers that possess specific characteristics, in phase, amplitude, or frequency index, corresponding to the cell associated with the base station, the cell-specific pilot subcarriers enabling a mobile station in the cell to determine cell-specific channel coefficients and apply the cell-specific channel coefficients to signals on the cell-specific data subcarriers received by the mobile station to compensate for cell-specific channel effects and recover cell-specific data carried by the cell-specific data subcarriers, wherein the cell-specific channel corresponds to the channel from the base station in the cell to the mobile station;

wherein;

the common pilot subcarriers generated by the base station and common pilot subcarriers generated by the other base stations in the system are aligned in frequency subcarrier index, and at least some of the cell-specific pilot subcarriers generated by the base station are not aligned in frequency subcarrier index with cell-specific pilot subcarriers generated by the other base stations; and

the common data subcarriers generated by the base station and common data subcarriers generated by the other base stations in the system are aligned in frequency subcarrier index, and at least some of the cell-specific data subcarriers generated by the base station are not aligned in frequency subcarrier index with cell-specific data subcarriers generated by the other base stations.

12. The method of claim 11, wherein cell-specific pilot subcarriers of the same frequency indices as cell-specific pilot subcarriers generated by adjacent base stations are not transmitted at the same time.

13. The method of claim 11, further comprising applying power control to the common pilot subcarriers, the cell-specific pilot subcarriers, or both, by adjusting the power of the corresponding pilot subcarriers individually or in subgroups.

14. The method of claim 11, wherein a phase difference between two common pilot subcarriers adjacent in frequency is the same for each of the plurality of base stations, and wherein a phase difference between two common pilot subcarriers adjacent in time is the same for each of the plurality of base stations.

15. The method of claim 11, wherein the specific amplitudes, phases, and frequency subcarrier indices of the cell-specific pilot subcarriers enable a mobile station in the cell to differentiate the cell-specific pilot subcarriers from cell-specific pilot subcarriers transmitted by base stations in other cells.

16. The method of claim 11, wherein within the plurality of cells, groups of two or more cells are associated together to form a plurality of groups of cells,

the common data subcarriers further generated so that they carry data common to the cell group that the base station is associated with, but different from other cell groups;

and

the common pilot subcarriers further generated so that they possess characteristics common to the cell group that the base station is associated with, but different from other cell groups.

17. The method of claim 11, wherein at least part of the common pilot subcarriers, the cell-specific pilot subcarriers, or both, enable a mobile station in the system to perform frame synchronization, frequency offset estimation, or timing estimation.

18. The method of claim 11, wherein the common pilot subcarriers are transmitted on different antennas such that a phase difference between two common pilot subcarriers adjacent in frequency is the same for each antenna and a phase difference between two common pilot subcarriers adjacent in time is the same for each antenna.

19. The method of claim 18, further comprising applying power control to the common pilot subcarriers on each antenna by adjusting the power of the common pilot subcarriers individually or in groups.

20. The method of claim 11, further comprising generating the subcarriers in an orthogonal frequency division multiple access signal or a multi-carrier code-division multiple access signal.

21. A method of receiving frequency subcarriers by a mobile station in a multi-carrier multi-cell wireless communication system comprised of a plurality of mobile stations and base stations in a plurality of cells, the mobile station associated with a serving base station in a serving cell and including a receiver configured to receive different types of subcarriers within a same frequency band that is divided into a plurality of subcarriers, the method comprising:

receiving common data subcarriers that carry data common to the plurality of cells, the common data subcarriers transmitted by the serving base station being aligned in frequency subcarrier index with common data subcarriers transmitted by other base stations in the system;

receiving common pilot subcarriers that possess characteristics common to the plurality of cells, the common pilot subcarriers transmitted by the serving base station being aligned in frequency subcarrier index with common pilot subcarriers transmitted by the other base stations in the system;

receiving cell-specific data subcarriers that carry data specific to the serving cell,

at least some of the cell-specific data subcarriers transmitted by the serving base station being not aligned in frequency subcarrier index with cell-specific data subcarriers transmitted by the other base stations in the system; and

receiving cell-specific pilot subcarriers that possess specific characteristics, in phase, amplitude, or frequency subcarrier index, corresponding to the serving cell, at least some of the cell-specific pilot subcarriers transmitted by the serving base station being not aligned in frequency subcarrier index with cell-specific pilot subcarriers transmitted by the other base stations in the system;

wherein;

composite channel coefficients are determined based on received signals on

the common pilot subcarriers and applied to received signals on the common data subcarriers to compensate for composite channel effects and to recover the common data carried on the common data subcarriers, wherein the composite channel corresponds to an aggregate of different

channels from the plurality of base stations to the mobile station; and

cell-specific channel coefficients are determined based on received signals on the cell-specific pilot subcarriers and applied to received signals on cell-specific data subcarriers to compensate for cell-specific channel effects and to recover cell-specific data carried on the cell-specific data subcarriers, wherein the cell-specific channel corresponds to the channel from the serving base station to the mobile station.

22. The method of claim 21, wherein a frequency of the signals received from the serving base station are estimated using common pilot subcarriers received at a first and a second time.

23. The method of claim 21, wherein a sampling period of the signals received from the serving base station are estimated using common pilot subcarriers received at a first and a second frequency indices.

24. The method of claim 21, further comprising determining frame synchronization, frequency offset estimation, or timing estimation based on the cell-specific subcarriers, the common pilot subcarriers, or both.

25. The method of claim 24, further comprising estimating a frequency offset based on the common pilot subcarriers, wherein the estimation is carried out in the time domain.

26. The method of claim 25, further comprising improving the accuracy of the frequency offset estimation based on the cell-specific pilot subcarriers, the common pilot subcarriers, or both, wherein the estimation is carried out in the frequency domain.

27. The method of claim 21, further comprising differentiating the cell-specific pilot subcarriers, based on their amplitudes, phases, and frequency subcarrier indices, from cell-specific pilot subcarriers transmitted by base stations in other cells.

28. The method of claim 21, wherein the subcarriers are received in an orthogonal frequency division multiple access signal or a multi-carrier code-division multiple access signal.

29. A base station in a multi-carrier, multi-cell, wireless communication system comprised of a plurality of mobile stations and base stations in a plurality of cells, the base station associated with a cell in the plurality of cells, including a transmitter that is synchronized in time and frequency with transmitters in other base stations in the system, and configured for transmitting common pilot subcarriers, common data subcarriers, cell-specific pilot subcarriers, and cell-specific data subcarriers within a same frequency band that is divided into a plurality of subcarriers,

wherein:

the common pilot subcarriers possess characteristics common to the plurality of cells, and the cell-specific pilot subcarriers possess specific characteristics, in phase, amplitude, or frequency index, corresponding to the cell;

the common pilot subcarriers transmitted by the base station are aligned in frequency subcarrier index with common pilot subcarriers transmitted by the other base stations in the system, and at least some of the cell-specific pilot subcarriers transmitted by the base station are not aligned in frequency subcarrier index with cell-specific pilot subcarriers transmitted by the other base stations in the system;

the common data subcarriers carry data common to the plurality of cells, and the cell-specific data subcarriers carry data specific to the cell; and

the common data subcarriers transmitted by the base station are aligned in frequency subcarrier index with common data subcarriers transmitted by the other base stations in the system, and at least some of the cell-specific data subcarriers transmitted by the base station are not aligned in frequency subcarrier index with cell-specific data subcarriers transmitted by the other base stations in the system.

30. A mobile station in a multi-carrier, multi-cell, wireless

communication system comprised of a plurality of mobile stations and base stations in a plurality of cells, the mobile station including a receiver configured for receiving, within a same frequency band that is divided into a plurality of subcarriers, cell-specific pilot subcarriers and cell-specific data subcarriers transmitted from a serving base station in a serving cell in which the mobile station is associated, and common pilot subcarriers and common data subcarriers transmitted from the serving base station and other base stations in the system, wherein:

the common pilot subcarriers possess characteristics common to the plurality of cells, and the cell-specific pilot subcarriers possess specific characteristics, in phase, amplitude, or frequency index, corresponding to the serving cell;

the common pilot subcarriers transmitted by the serving base station are aligned in frequency subcarrier index with common pilot subcarriers transmitted by other base stations in the system, and at least some of the cell-specific pilot subcarriers transmitted by the serving base station are not aligned in frequency subcarrier index with cell-specific pilot subcarriers transmitted by the other base stations in the system;

the common data subcarriers carry data common to the plurality of cells, and the cell-specific data subcarriers carry data specific to the serving cell; and

the common data subcarriers transmitted by the serving base station are aligned in frequency subcarrier index with common data subcarriers transmitted by the other base stations in the system, and at least some of the cell-specific data subcarriers transmitted by the serving base station are not aligned in frequency subcarrier index with cell-specific data subcarriers transmitted by the other base stations.