Method and system for allocating subcarriers to subscriber devices

• US 7,586,990 B2
• Filed: 11/22/2005
• Issued: 09/08/2009
• Est. Priority Date: 11/22/2005
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.), Northwestern University
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.), Northwestern University
• Inventors: Huang, Jiawei, Agrawal, Rajeev, Subramanian, Vijay G., Berry, Randall
• Primary Examiner(s): Ghayour; Mohammad H
• Assistant Examiner(s): Hassan; Sarah
• Application Number:
  US11/286,944
• Publication Number:
  US 20070116139A1
• Time in Patent Office: 1,386 Days
• Field of Search: 375/260, 375/316
• US Class Current: 375/260
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

Abstract

A method and system for allocating a plurality of subcarriers to a plurality of subscriber devices in a wireless network. A set of characteristics is identified (302) for a transmission on each of the plurality of subcarriers. A dynamic weight is assigned (304) to at least one subscriber device of the plurality of subscriber devices at each decision instance of the transmission corresponding to the at least subscriber device. The assignment of the dynamic weight is based on at least one of a throughput, delay, packet-loss and queue length requirement of one or more flows of the subscriber device. Further, a set of optimum values is determined (306) for the set of characteristics based on the dynamic weights and channel feedback. The plurality of subcarriers are allocated (308) to the at least one subscriber device based on at least one optimum value of the set of optimum values.

Claims

1. A method for allocating a plurality of subcarriers to a plurality of subscriber devices in a wireless network, the method comprising:

identifying a power for a transmission on each subcarrier of the plurality of subcarriers;

assigning a dynamic weight to at least one subscriber device of the plurality of subscriber devices at each decision instance of the transmission corresponding to the at least subscriber device, wherein the assignment of the dynamic weight is based on queue length requirements of one or more flows of the at least one subscriber device;

determining a set of optimum values for the power based on the dynamic weight, wherein the set of optimum values are determined under a set of constraints for each subcarrier of the plurality of subcarriers, and comprising optimizing a rate vector V_t, of the form

$V_t=\arg <br><br><br><br>\underset{v<br><br><br><br>\mathrm{\epsilon <br><br>}<br><br><br><br>R<br><br>\left({\mathrm{\eta <br><br>}}_t\right)}{\max }<br><br>\underset{i}{\sum <br><br>}<br><br>w_i<br><br>v_i$

where η

_t represents the collective (of all users) channel state at time t, R(η

_t) is the rate region at time t, v_i is a rate for the subscriber device S_i and w_i, is the dynamic weight assigned to v_i; and

allocating at least one subcarrier of the plurality of subcarriers to at least one subscriber device based on at least one optimum value of the set of optimum values.

2. The method according to claim 1 further comprising allocating an optimal power to at least one subcarrier.

3. The method according to claim 1 wherein the set of constraints for each subcarrier of the plurality of subcarriers is at least one from a group comprising uplink constraints, downlink constraints, and subscriber device constraints.

4. The method according to claim 1 wherein the dynamic weight is a collective dynamic weight of different dynamic weights for each flow from the at least one subscriber device.

5. The method according to claim 1 wherein for an OFDMA downlink the rate vector for which the carrier channel includes M subcarriers represented by {C₁, . . . , C_i, . . . C_M} takes the form

$\underset{0\le \; <li></li>p_{\mathrm{ij}}\le <br><br>\frac{x_{\mathrm{ij}}<br><br>s_{\mathrm{ij}}}{e_{\mathrm{ij}}},0\le <br><br>x_{\mathrm{ij}}\le <br><br>1}{\max }<br><br>\underset{i,j}{\sum <br><br>}<br><br>w_i<br><br>x_{\mathrm{ij}}<br><br>\log <br><br>\left(1+\frac{p_{\mathrm{ij}}<br><br>e_{\mathrm{ij}}}{x_{\mathrm{ij}}}\right)<br><br>\mathrm{subject}<br><br><br><br>\mathrm{to}<br><br><br><br>\underset{i,j}{\sum <br><br>}<br><br>p_{\mathrm{ij}}\le <br><br>P,\underset{i}{\sum <br><br>}<br><br>x_{\mathrm{ij}}\le <br><br>1<br><br>\forall <br><br>j$

where P_ij is the power for the subscriber device S_i in the subcarrier C_j, x_ij is the fraction of C_j used by S_i, e_ij is the channel state or condition for S_i in C_j. For example, e_ij can be the normalized SINR for S_i in C_j. Also, s_ij is the maximum SINR for S_i in C_j.

6. The method according to claim 5 wherein the rate vector is optimized using one or more Lagrange multipliers comprising a first Lagrange multiplier and a subscriber metric for each subcarrier of the plurality of subcarriers, where

$\mathrm{reduces}$

⁢

to ⁢

⁢

max 0 ≤

p ij ≤

x ij ⁢

s ij e ij , 0 ≤

x ij ≤

1 ⁢

∑

i , j ⁢

w i ⁢

x ij ⁢

log ⁡

( 1 + p ij ⁢

e ij x ij ) ⁢

min ⁢

λ

≥

0 , μ

≥

0 ⁢

⁢

max 0 ≤

p ≤

xs e , 0 ≤

x ≤

1 ⁢

L ⁡

( p , x , λ

, μ

)

where L(p,x,λ

,μ

) is the Lagrangian given by

$L<br><br>\left(p,x,\mathrm{\lambda <br><br>},\mathrm{\mu <br><br>}\right)=\underset{i,j}{\sum <br><br>}<br><br>w_i<br><br>x_{\mathrm{ij}}<br><br>\log <br><br>\left(1+\frac{p_{\mathrm{ij}}<br><br>e_{\mathrm{ij}}}{x_{\mathrm{ij}}}\right)+\mathrm{\lambda <br><br>}<br><br>\left(P-\underset{i,j}{\sum <br><br>}<br><br>p_{i,j}\right)+\underset{j}{\sum <br><br>}<br><br>{\mathrm{\mu <br><br>}}_j<br><br>\left(1-\underset{i}{\sum <br><br>}<br><br>x_{i,j}\right)$

where λ and

μ

are the Lagrange multipliers. Here p denotes the matrix of p_ij for all i and j, and x, s and e are similarly defined. λ

is a first Lagrange multiplier, and μ

is redefined as a subscriber metric μ

is given as

μ

_ij=w_ih(λ

,w_i,e_ij,s_ij)

where h( ) is a computable function, s_ij is the maximum SINR for S_i in C_j, and e_ij is obtained from channel feedback.

7. The method according to claim 6 wherein the subscriber metric is estimated by determining a minimum value of the first Lagrange multiplier.

8. The method according to claim 6 wherein the subscriber metric is estimated by using an arbitrary value of the first Lagrange multiplier.

9. The method according to claim 8 wherein the arbitrary value is based on the dynamic weight, and at least one set of constraints from the group consisting of uplink constraints and downlink constraints.

10. The method according to claim 6 wherein the subscriber metric is a function of at least one from a group comprising the dynamic weight, subcarrier usage, and signal to interference-plus-noise ratio (SINR) of the transmission.

11. The method according to claim 1 wherein allocating the at least one subcarrier of the plurality of subcarriers to the at least one subscriber device comprises allocating that subcarrier to the subscriber device for which a subscriber metric is maximum.

12. The method according to claim 1 wherein the transmission is directed from at least one subscriber device to a base station.

13. The method according to claim 1 wherein the transmission is directed from a base station to at least one subscriber device.

14. The method according to claim 1 wherein the at least one subcarrier is allocated to at least one subscriber device using interleaving.

15. The method according to claim 1 wherein the at least one subcarrier is allocated to at least one subscriber device using frequency-hopping.

16. The method according to claim 1 wherein a contiguous allocation is performed to allocate at least one subcarrier to the at least one subscriber device.

17. A method for optimizing subcarrier allocation for a plurality of subscriber devices in a wireless network, the method comprising:

identifying a power for transmissions on a plurality of subcarriers;

assigning a dynamic weight to one or more subscriber devices of the plurality of subscriber devices at each decision instance of a transmission corresponding to the one or more subscriber devices, wherein assignment of the dynamic weight is based on queue length requirements of one or more flows of the one or more subscriber devices;

determining a set of optimum values of the power for each subcarrier of the plurality of subcarriers based on the dynamic weight, wherein the set of optimum values are determined under a set of constraints for each subcarrier of the plurality of subcarriers, and comprising optimizing a rate vector V_t, of the form

$V_t=\arg <br><br><br><br>\underset{v<br><br><br><br>\mathrm{\epsilon <br><br>}<br><br><br><br>R<br><br>\left({\mathrm{\eta <br><br>}}_t\right)}{\max }<br><br>\underset{i}{\sum <br><br>}<br><br>w_i<br><br>v_i$

where η

_t represents the collective (of all users) channel state at time t, R(η

_t) is the rate region at time t, v_i is a rate for the subscriber device S_i, and w_i is the dynamic weight assigned to v_i;

grouping subcarriers of the plurality of subcarriers into a set of bundles based on the set of optimum values for each subcarrier of the plurality of subcarriers; and

allocating a bundle of the set of bundles to the one or more subscriber devices based on the set of optimum values for each subcarrier in the bundle.

18. The method according to claim 17 wherein grouping the subcarriers of the plurality of subcarriers into the set of bundles comprises grouping the subcarriers using at least one from a group comprising contiguous allocation, frequency hopping, and interleaving.

19. A system in a base station suitable for allocating a plurality of subcarriers to a plurality of subscriber devices in a wireless network, the system comprising:

an identifier capable of identifying a power for a transmission on each subcarrier of the plurality of subcarriers;

an assignor for assigning a dynamic weight to at least one subscriber device of the plurality of subscriber devices at each decision instance of the transmission corresponding to the at least one subscriber device, wherein assignment of the dynamic weight is based on queue length requirements of one or more flows of the at least one subscriber device;

an optimizer capable of determining a set of optimum values for the power based on the dynamic weight, wherein the set of optimum values are determined under a set of constraints for each subcarrier of the plurality of subcarriers, and comprising optimizing a rate vector V_t, of the form

$V_t=\arg <br><br><br><br>\underset{v<br><br><br><br>\mathrm{\epsilon <br><br>}<br><br><br><br>R<br><br>\left({\mathrm{\eta <br><br>}}_t\right)}{\max }<br><br>\underset{i}{\sum <br><br>}<br><br>w_i<br><br>v_i$

where η

_t represents the collective (of all users) channel state at time t, R(η

_t) is the rate region at time t, v_i is a rate for the subscriber device S_i, and w_i is the dynamic weight assigned to v_i; and

an allocator capable of allocating at least one subcarrier of the plurality of subcarriers to at least one subscriber device based on at least one optimum value of the set of optimum values.