Systems and methods for channel allocation for forward-link multi-user systems

• US 20030227889A1
• Filed: 03/28/2003
• Published: 12/11/2003
• Est. Priority Date: 06/07/2002
• Status: Active Grant

• Current Assignee: Daniel Boudreau, Jianming Wu, Wen Tong
• Original Assignee: Apple Inc.
• Inventors: Wu, Jianming, Boudreau, Daniel, Tong, Wen
• Granted Patent: US 9,125,061 B2
• Time in Patent Office: Days
• US Class Current: 370/335
• CPC Class Codes: H04W 16/12 Fixed resource partitioning
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA
• CPC Class Codes: H04W 72/535 based on resource usage policies

Abstract

A method of allocating bandwidth is provided which involves for each sector of a plurality of sectors in a cell, using a respective subset of a total bandwidth; wherein for any two adjacent sectors, the respective subsets only partially overlap. A scheduling method is provided which involves for each sector, scheduling users for transmission on the respective subset of the total bandwidth by: for a given transmitter, allocating a respective fraction of capacity associated with the available bandwidth to each of at least two users selected from a plurality of users by performing an optimization for a selected scheduler design, the optimization selecting the at least two users and the optimization determining for each user the respective fraction of capacity; generating and transmitting a signal in which each of the at least two users has the respective fraction of capacity.

Claims

1. A method of allocating bandwidth comprising:

for each sector of a plurality of sectors in a cell, using a respective subset of a total bandwidth;

wherein for any two adjacent sectors, the respective subsets only partially overlap.

2. A method according to claim 1 comprising:

for each cell, sub-dividing the total frequency bandwidth into a plurality of fixed sub-bands;

for each sector, allocating the respective subset to be at least two of the fixed sub-bands.

3. A method according to claim 1 wherein the fixed sub-bands are equal in size.

4. A method according to claim 1 further comprising:

in each sector, transmitting a respective user transmission on each of the sub-bands.

5. A method according to claim 1 further comprising:

for pairs of sectors that face each other of different cells, allocating respective subsets which only partially overlap.

6. A method according to claim 1 for application in three sector cells, wherein two thirds of the total frequency bandwidth is allocated to each of the three sectors such that each sector shares one third of the total frequency bandwidth with each adjacent sector.

7. A method according to claim 1 further comprising:

for each sector, scheduling users for transmission on the respective subset of the total bandwidth by;

for a given transmitter, allocating a respective fraction of capacity associated with the available bandwidth to each of at least two users selected from a plurality of users by performing an optimization for a selected scheduler design, the optimization selecting the at least two users and the optimization determining for each user the respective fraction of capacity;

generating and transmitting a signal in which each of the at least two users has the respective fraction of capacity.

8. A method according to claim 7 wherein the optimization is performed every transmission interval, and the optimization maximizes sector throughput.

9. A method according to claim 7 wherein the scheduler design is selected from a group comprising:

proportional fairness, proportional fairness for FTP traffic, adaptive scheduler, adaptive scheduler for video service.

10. A method according to claim 7 wherein the optimization performs a maximization of proportional factors relative to user transmission rate and average user throughput, while keeping a total frequency bandwidth constant.

11. A method according to claim 7 further comprising in performing the optimization, using an unconstrained optimization obtained by using a Lagrangian of a constrained optimization.

12. A method according to claim 7 wherein the optimization comprises:

for each pair of users indicated by k₀ and k₁ associating respective F_i0 and F_i1, and respective bandwidths of

$W_{k_0}^{\left(F_{\mathrm{i0}}\right)}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>W_{k_1}^{\left(F_{\mathrm{i1}}\right)};<br><br>$

determining a transmission rate for each selected user in each slot to be R_k0 and R_k1, when using the available frequency bandwidth W, and with sub-bandwidths of

$W_{k_0}^{\left(F_{\mathrm{i0}}\right)}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>W_{k_1}^{\left(F_{\mathrm{i1}}\right)},$

determining transmission rates

$R_{k_0}^{\left(F_{\mathrm{i0}}\right)}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>R_{k_0}^{\left(F_{\mathrm{i1}}\right)}$

according to

$\begin{array}{c}{R}_{k_0}^{\left(F_{\mathrm{i0}}\right)}=R_{k_0}·<br><br>\frac{W_{k_0}^{\left(F_{\mathrm{i0}}\right)}}{W}\\ R_{k_1}^{\left(F_{\mathrm{i1}}\right)}=R_{k_1}·<br><br>\frac{W_{k_1}^{\left(F_{\mathrm{i1}}\right)}}{W}\end{array}$

performing optimization which maximizes sector throughput, applied to two users per sector or generalized to N users per sector, where N>

=3.

13. A method according to claim 12 wherein the optimization is formulated as follows:

14. A method according to claim 13 further comprising using a Lagrangian of the optimization to obtain the following unconstrained optimization formula:

15. A method according to claim 1 further comprising:

in each sector, transmitting an OFDM signal using the respective subset of the total OFDM bandwidth.

16. A method according to claim 15 wherein in each sector, transmitting an OFDM signal using the respective subset of the total OFDM bandwidth comprises:

generating the OFDM signal from content of at least two users.

17. A method according to claim 16 wherein in each sector generating the OFDM signal from content of at least two users comprises:

mapping symbols from each user into a time domain representation;

converting the time domain representation into the OFDM signal.

18. A method according to claim 17 wherein mapping symbols from each user into a time domain representation comprises interleaving.

19. A method according to claim 17 further comprising:

for each sector, performing an optimization to identify the at least two users, and to determine for each user a respective number of symbols to be mapped into said time domain representation.

20. A method of scheduling users for transmission on an available bandwidth comprising:

for a given transmitter, allocating a respective fraction of capacity associated with the available bandwidth to each of at least two users selected from a plurality of users by performing an optimization for a selected scheduler design, the optimization selecting the at least two users and the optimization determining for each user the respective fraction of capacity;

generating and transmitting a signal in which each of the at least two users has the respective fraction of capacity.

21. A method according to claim 20 wherein the optimization is performed every transmission interval, and the optimization maximizes sector throughput.

22. A method according to claim 20 wherein the scheduler design is selected from a group comprising:

proportional fairness, proportional fairness for FTP traffic, adaptive scheduler, adaptive scheduler for video service.

23. A method according to claim 20 wherein the optimization performs a maximization of proportional factors relative to user transmission rate and average user throughput, while keeping a total frequency bandwidth constant.

24. A method according to claim 23 further comprising in performing the optimization, using an unconstrained optimization obtained by using a Lagrangian of a constrained optimization.

25. A method according to claim 20 wherein the signal is an OFDM signal, the method further comprising generating the OFDM signal from content of at least two users by mapping with interleaving bits from each user into a time domain representation and converting the time domain representation into the OFDM signal.

26. A method according to claim 25 wherein for each sector, the optimization determines for each of the selected users a respective number of symbols to be mapped into the time domain representation, the respective number of symbols comprising said respective fraction of capacity.

27. A method according to claim 25 wherein the optimization performs a maximization of proportional factors relative to user transmission rate and average user throughput, while keeping a total frequency bandwidth constant.

28. A method according to claim 25 wherein the optimization comprises:

for each pair of users indicated by k₀ and k₁ with respective sub-bandwidths of W_k0 and W_k1, determining a transmission rate for each user in each slot to be R_k0 and R_k1, when using the available frequency bandwidth W, and with sub-bandwidths of W_k0 and W_k1, the transmission rates R_k0 and R_k0 are given by

$R_{k_0}=R_{k_0}·<br><br>\frac{W_{k_0}}{W}$

performing optimization which maximizes sector throughput.

29. A method according to claim 28 generalized to schedule N users per sector, where N>

=3.

30. A method according to claim 28 further comprising:

receiving a channel quality indication from each user being considered for scheduling;

for each permutation of two users, calculating transmission rates according to adaptive modulation and coding as a function of the channel quality indications and using the calculated transmission rates in the optimization

31. A method according to claim 30 wherein the channel quality indications comprise SNR (signal-to-noise ratio) values.

32. A method according to claim 28 wherein the optimization is formulated as follows:

33. A method according to claim 32 generalized to schedule N users in the transmission interval, where N>

=3.

34. A method according to claim 32 further comprising using a Lagrangian of the optimization to obtain the following unconstrained optimization formula:

35. A method according to claim 32 generalized to schedule N users in the transmission interval, where N>

=3.

36. A method according to claim 20 further comprising allocating bandwidth by:

for each sector of a plurality of sectors in a cell, using a respective subset of a total bandwidth;

wherein for any two adjacent sectors, the respective subsets only partially overlap.

37. A method according to claim 20 wherein said signal is a CDMA signal, the method further comprising generating the CDMA signal from content of at least two users by modulating content of each user to a respective subset of a set of orthogonal codes.

38. A method according to claim 37 wherein for each sector, the optimization determines for each of the at least two users a respective number of orthogonal codes in the respective subset, the respective number of orthogonal codes comprising said respective fraction of capacity.

39. A method according to claim 38 wherein the optimization performs a maximization of proportional factors relative to user transmission rate and average user throughput, while keeping the total frequency bandwidth constant.

40. A method according to claim 38 wherein two users indicated by k₀ and k₁ are to be selected to transmit data with a number of Walsh codes

41. A method according to claim 40 generalized to schedule M users each scheduling period.

42. A method according to claim 40 wherein proportional fairness as a user scheduler is employed, and the optimization maximizes a proportional factor relative to user transmission rate and average user throughput, while keeping the total number of orthogonal codes constant.

43. A method according to claim 42 wherein the optimization is be formulated as follows:

44. A method according to claim 43 further comprising using a Lagrangian of the optimization of claim 40 to obtain the following unconstrained optimization formula:

45. A method according to claim 37 wherein the orthogonal codes are Walsh codes.

46. An apparatus comprising:

a respective transmitter and antenna for each sector of a plurality of sectors in a cell, each transmitter using a respective subset of a total bandwidth, wherein for any two adjacent sectors, the respective subsets only partially overlap.

47. A apparatus according to claim 46 wherein each transmitter is adapted to transmitting a respective user transmission on each of the sub-bands.

48. An apparatus according to claim 46 further comprising an optimization process adapted to for each sector, scheduling users for transmission on the respective subset of the total bandwidth by:

for a given transmitter, allocating a respective fraction of capacity associated with the available bandwidth to each of at least two users selected from a plurality of users by performing an optimization for a selected scheduler design, the optimization selecting the at least two users and the optimization determining for each user the respective fraction of capacity.

49. An apparatus according to claim 48 wherein the optimization process uses an unconstrained optimization obtained by using a Lagrangian of a constrained optimization.

50. An apparatus according to claim 46 wherein each transmitter comprises a respective OFDM transmitter adapted to generate a respective OFDM signal using the respective subset of the total bandwidth.

51. An apparatus according to claim 50 wherein each OFDM signal is generated from content of at least two users.

52. An apparatus according to claim 50 further comprising:

a symbol selector for selecting symbols for each of the at least two users;

an interleaver for mapping the bits from the at least two users to a time domain representation;

an IFFT function for converting the time domain representation into the OFDM signal.

53. An apparatus according to claim 50 further comprising an optimizer for performing an optimization in each sector to identify the at least two users, and for each user a respective fraction of symbols to be mapped into said time domain representation.

54. An apparatus comprising:

an optimizer adapted to scheduling users for transmission on a respective available bandwidth for each antenna by for a given transmitter, allocating a respective fraction of capacity associated with the available bandwidth to each of at least two users selected from a plurality of users by performing an optimization for a selected scheduler design, the optimization selecting the at least two users and the optimization determining for each user the respective fraction of capacity;

signal generation circuitry for generating a signal in which each of the at least two users have the respective fraction of capacity;

a transmitter for transmitting the signal.

55. An apparatus according to claim 54 wherein said signal is an OFDM signal, said signal generation circuitry comprises a symbol selector for selecting symbols for each user and mapping them to a time domain representation, and an IFFT function for mapping the time domain representation into a frequency domain representation.

56. An apparatus according to claim 54 forming part of a multi-sector transmitting apparatus in which for each sector of the multi-sector transmitting apparatus a respective subset of a total bandwidth is used, wherein for any two adjacent sectors, the respective subsets only partially overlap.

57. An apparatus according to claim 54 wherein said signal is a CDMA signal, the apparatus comprising:

a plurality of Walsh code spreaders adapted to perform Walsh code spreading with a respective Walsh code of a set of Walsh codes, wherein the CDMA signal is generated from content of at least two users by modulating content of each user with a respective subset of the set of Walsh codes.

58. An apparatus according to claim 57 the optimizer determines for each of the at least two users a respective number of orthogonal codes in the respective subset, the respective number of orthogonal codes comprising said respective fraction of capacity.