This relates generally to wireless communications and, particularly, to the use of hybrid automatic repeat requests (HARQ) in wireless systems.
In order to reduce errors in communications between base stations and mobile stations in wireless networks, the mobile station sends a response to signals it receives to indicate whether or not there were errors in the received signal. The communication channel from the base station to the mobile station, called the downlink, may include hybrid automatic repeat request (HARQ) packets. The channel from the mobile station to the base station, called the uplink, provides either an acknowledgement (ACK) or a negative acknowledgement (NAK) if errors were contained in the transmission.
Basically, in HARQ, error detection information bits are added to the data to be transmitted. Based on these bits, the mobile station can determine whether it received the information transmitted from the base station correctly. It sends an acknowledgement if it did receive them correctly and a negative acknowledgement if it did not.
A HARQ region is designed using three distributed feedback mini-tile (FMT), each having two sub-carriers by six Orthogonal Frequency Division Multiplexing (OFDM) symbols. A code division multiplexed based method has been proposed, but it has been found that a pure code division multiplexed based approach may have error floors for high mobility scenarios, especially with parallel multi-user transmissions. A time division multiplexed/frequency division multiplexed based method has also been proposed. In time division multiplexed/frequency division multiplexed designs, one HARQ feedback region is split into six orthogonal HARQ feedback channels using time division or frequency division multiplexing. Each HARQ feedback channel includes three units having one sub-carrier by two OFDM symbols. An orthogonal sequence of length two may be used to convey the one bit acknowledge negative acknowledge information. The time division/frequency division multiplexing design can overcome the error floor in high mobility scenarios. Moreover, the performance is robust to mobile station moving speed.
A hybrid time division, frequency division, code division multiplexing method can achieve similar performance and also is robust to high mobility. However, the major drawback to time division/frequency division multiplexed designs is that the distributed transmission power in the original design concentrates on three tiles and, thus, may cause interference to other cells.
Referring to
The mobile station 12 may include a radio frequency receiver 18, coupled to an OFDM demodulator 20. The OFDM demodulator may be coupled to a symbol demodulator 22, which may handle sub-carrier de-mapping. The symbol demodulator 22 may be coupled to an HARQ buffer 30. It may also be coupled to a decoder 24. An error check 26 determines whether there is an error in the HARQ enabled packets received on the downlink channel 16 and communicates with the HARQ buffer 30 to so indicate, as well as the controller 28.
On the transmit side, the controller 28 communicates with an encoder 32 and also communicates with the HARQ buffer 30. The encoder 32 is coupled to a symbol modulator 34 that also handles sub-carrier mapping. The symbol modulator is coupled to an OFDM modulator 36 that, in turn, is coupled to an RF transmitter 38.
In accordance with some embodiments of the present invention, the cell interference is randomized in order to ensure robust performance in multi-cell operation scenarios as indicated in
Since the time division (TDM)/frequency division (FDM) multiplexing or time division/frequency division/code division (CDM) multiplexing method is applied to the uplink HARQ feedback region, the second level may be inside the uplink HARQ feedback region (
The control channel permutation (
The HARQ ACK channel permutation can be generalized as follows. Firstly, index the sub-carrier of one HARQ channel as
The total 36 sub-carriers can be further divided into 18 units, each having 1 sub-carrier by 2 contiguous OFDM symbols. There are two types of units, as shown in FIGS. 2 and 3, respectively. The unit shown in
The remaining 18 units are for the Type 2 units and the sub-carrier positions can be written as equation 2 shown as below:
The sub-carrier positions of 6 HARQ ACK channels can be described using 3 units Rn=(Qj
There are in total 64 positions for the 0th HARQ ACK channel and it can be defined as below equation:
R0ε{(Q{0,18},Q{8,9,24,25},Q{16,17,34,35}),(Q{0,18},Q{14,15,32,33},Q{10,11,28,29})} (3)
Denote the first half of R0 as Ψ0′={(Q{0,18},Q{8 ,9,24,25},Q{16,17,34,35})} and the second half of R0 as Ψ0″={(Q{0,18},Q{14,15,32,33},Q{10,11,28,29})}. The positions of the rest of the HARQ ACK channels depend on the positions of the first HARQ ACK channel:
R
0εΨ2′={(Q{6,24},Q{14,15,30,31},Q{4,5,22,23})} (4)
R
4εΨ4′={(Q{12,30},Q{2,3,20,21},Q{10,11,28,29})} (5)
R
2εΨ2″={(Q{6,24},Q{2,3,20,21},Q{16,17,34,35})} (6)
R
4εΨ4″={(Q{12,30},Q{8,9,26,27},Q{4,5,22,23})} (7)
The positions of the three odd HARQ ACK channels can be inferred from the positions of three even HARQ ACK channels:
R
2u+1=(Qj
where j2u+1,m=└j2u,m/2┘×4+1−j2u,m,0≦u<3,0≦m<3
So, in total for one type of unit, there are 65536 types of HARQ ACK channel permutation patterns in one HARQ ACK channel. One HARQ ACK channel permutation pattern can be uniquely represented by one index S where 0≦S<216. S can be represented in binary as a0, a1, a2, . . . , a15. The first bit a0 is subset selection bit.
If a0=0
R0εΨ0′, R2εΨ2′, R4εΨ4′
Else
R0εΨ0″, R2εΨ2″, R4εΨ4″
End.
The following 5 bits a1, a2, . . . , a5 can be used to describe the positions of HARQ ACK channel O. When the permutation pattern index a1, a2, . . . , a5=‘00000’, the permutation pattern is selected by the first combination of Ψ0′ or Ψ0″, e.g. R0=(Q0,Q8,Q16) or R0=(Q0,Q14,Q10). If the permutation pattern index a1, a2, . . . , a5=‘00001’, the permutation pattern is selected by the second combination of Ψ0′ or Ψ0″, e.g. R0(Q0,Q8,Q17) or R0=(Q0,Q14,Q11). Similarly, bits a6, a7, . . . , a10 and a11, a12, . . . , a15 are used to describe the positions of HARQ ACK channels 2 and 4 in a similar way, respectively.
For a given section, S can change in time and the changing patterns for different sectors can be different to maximize interference randomization. One example of changing pattern of S is a pseudo random number with sector specific random number state. Or S can be planned among sectors. The planning of S can be done by planning the 16 bits of HARQ channel permutation pattern. One example of planning uses a network example, given in
a0=sid mod 2
a1, a2, . . . , a5 can be planned according to a table: [23 30 7 20 24 14 26 29 25 1 28 21 15 18 9 6 3 27 2 10 13 31 5 11 22 8 4 19 17 12 16 0] and the reuse distance is 32. For a given sector, a1, a2, . . . , a5 should be the index sid mod 32 in above table.
a6, a7, . . . , a10 and a11, a12, . . . a15 can be planned accordingly.
For TDM/FDM/CDM method, there is one method to map one HARQ unit to physical sub-carriers as shown in
Qj=(Qj0, Qj1, Qj2, Qj3),0≦j<9 where j is unit index, Qjs,0≦s<4 is sub-carrier position of sth sub-carrier of unit j. There is only one type of unit, as shown in
Q
j
s
=P
12└ji3┘+4·(j mod 3)+s,0≦j<9,0≦s<4 (10)
There are in total two unit indexes for the first two HARQ ACK channel and it can be defined as below equation:
R
0
=R
1ε{(Q0,Q4,Q8),(Q0,Q7,Q5)} (11)
If R0=(Q0, Q4,Q8), the positions of the rest of the four HARQ ACK channels can be described as below two equations:
R
2
=R
3=(Q3,Q7,Q2) (12)
R
2
=R
3=(Q6,Q1,Q5) (13)
If R0=(Q0, Q7, Q5), the positions of the rest of the four HARQ ACK channels can be described as below two equations:
R
2
=R
3=(Q3,Q1,Q8) (14)
R
4
=R
5=(Q6,Q4,Q2) (15)
So, in total for one type of unit, there are two types of HARQ ACK channel permutation patterns in one HARQ ACK channel. One bit is enough to describe the ACK channel permutation.
The HARQ sub-channel index permutation (
Alternatively, the channel index can be planned if there is enough information to perform inter sector coordination. Using the network example in
PhyChanId=(Log ChanId+sid*2)mod 6 (16)
This equation assumes, upon allocation of logical ACK channel index, each base station will allocate from lowest available logical ACK channel index or highest available logical ACK channel index. Then when load is low, inter-cell ACK interference can be orthogonal in time-frequency domain.
The HARQ sequence permutation (
PhaseIdx=sid mod 8 (17)
In some embodiments, the sequence depicted in
In some embodiments, the radios depicted herein as the base station and the mobile station can include one or more than one antennae. In one embodiment, the mobile station and the base station may include one transmit antenna and two receive antennas.
References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
This application claims priority to provisional application 61/142,582, filed Jan. 5, 2009, hereby expressly incorporated by reference herein.
Number | Date | Country | |
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61142582 | Jan 2009 | US |