Method and system for power controlled effective allocation of sub-bands in ultra-wideband communication

• US 20070091983A1
• Filed: 05/31/2006
• Published: 04/26/2007
• Est. Priority Date: 06/01/2005
• Status: Active Grant

• Current Assignee: University of Maryland
• Original Assignee: University of Maryland
• Inventors: Siriwongpairat, Wipawee, Han, Zhu, Liu, K.J.
• Granted Patent: US 7,653,122 B2
• Time in Patent Office: Days
• US Class Current: 375/130
• CPC Class Codes: H04B 1/71632 Signal aspects H04B1/7172 and H04B1/7176 take precedence
• CPC Class Codes: H04B 1/719 Interference-related aspects
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0039 Frequency-contiguous, i.e. with no allocation of frequencies for one user or terminal between the frequencies allocated to another
• CPC Class Codes: H04L 5/0064 Rate requirement of the data, e.g. scalable bandwidth, data priority
• CPC Class Codes: H04L 5/0075 Allocation using proportional fairness

Abstract

A power controlled sub-band assignment and power allocation among users in a multiband UWB system aims to reduce power consumption without compromising performance. The overall transmit power is minimized under the practical constraints, including packet error rate, transmission rate, and FCC regulations. To insure the system feasibility in variable channel conditions, an optimization scheme manages the assignment of UWB devices to respective channels subject to their suitability to the requested users'"'"' transmission rates. An inexpensive suboptimal approach reduces the complexity of the optimization procedure and achieves a comparable performance to those of the complex full search optimization routine. The suboptimal scheme obtains the feasible solutions adaptively when the channels assignment, initially calculated under the optimization criteria, is not feasible for the user'"'"'s rate requirement.

Claims

1. A method for power efficient channel allocation in a multi-band multi-user ultra-wideband (UWB) system, including a plurality of K users, a plurality of S sub-bands, and a plurality of N sub-carriers, wherein each k^th of said plurality of K users requests transmission with a data transmission rate R_k, including the steps of:

defining a sub-band assignment matrix A including a plurality of a_ks elements, wherein k=1, 2, . . . , k, and s=1, 2, . . . , S, said a_ks represents the duration of a data packet which the k^th user is allowed to transmit on the s^th sub-band;

establishing a power allocation matrix P including a plurality of P_k^s elements, each P_k^s representing the transmit power of the k^th user at each sub-carrier of the s^th sub-band;

calculating said sub-band assignment matrix A and said power allocation matrix P under pre-defined constraints to allocate the users'"'"' transmissions to respective sub-bands, thereby minimizing the overall transmit power in said UWB system; and

,

adapting said sub-band assignment matrix A and said power allocation matrix P to said respective sub-bands'"'"' conditions, if said allocation of the users'"'"' transmissions to said respective sub-bands deviates from a predetermined allocation criteria.

2. The method of claim 1, further comprising the steps of:

assigning a respective sub-band to a respective one of said plurality of including the steps of;

(a) setting said sub-band assignment matrix A=0<sub>k×

s</sub>;

(b) defining user optimization list K_live={1, 2, . . . , K};

(c) defining sub-band optimization list S_live={1, 2, . . . , S};

(d) calculating a dummy overall transmission power P_dummy^k for each k^th user of said plurality of k users wherein P_dummy^k=min Σ

_s=1^Sa_ks^P_k^s, s ε

S_live;

(e) assigning said respective sub-band to a user k with the highest P_dummy^k, and removing said user k from said user optimization list K_live;

(f) removing said assigned respective sub-band from said sub-band optimization list S_live;

(g) repeating said steps (d)-(f) for remaining users in said user optimization list K_live, until said K_live=0, thereby assigning transmissions of said plurality K of the users to said plurality of S sub-bands in said sub-band optimization list S_live; and

(h) comparing a transmit power for each assigned sub-band to a pre-determined maximum power value.

3. The method of claim 2, further comprising the steps of:

indicating an outage if the transmit power for said each assigned sub-band is larger than said pre-determined maximum power value; and

adapting said requested data transmission rate R_k of at least one user of said plurality of K users.

4. The method of claim 2, further comprising the step of:

indicating on outage if S_live=0 and K_live≠

0.

5. The method of claim 2, further comprising the step of:

accepting said calculated sub-band assignment matrix A and said power allocation matrix P as optimal if said transmit power for each said assigned sub-band does not exceed said pre-determined maximum power value.

6. The method of claim 3i further comprising the steps of:

(i) in said step of said requested data transmission rate R_k adaptation, choosing a single k^th user,

(j) reducing said single k^th user'"'"'s data transmission rate to a one-step reduced data transmission rate R_k⁻

;

(k) repeating said steps (d)-(h); and

(l) repeating said steps (i)-(k) for the remaining users in said plurality of K users.

7. The method of claim 6, further comprising the steps of:

choosing said k^th users in accordance with performance goals, including;

$\hat{k}=\{\begin{array}{cc}\arg <br><br>\text{\hspace{1em}<br><br>}<br><br>{\max }_k<br><br>R_k^{-}+\underset{j=1,j\ne <br><br>k}{\overset{K}{\sum <br><br>}}<br><br>R_j,& \mathrm{Maximizing}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{overall}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{rate};<br><br>\\ \arg <br><br>\text{\hspace{1em}<br><br>}<br><br>{\max }_k<br><br>\left(R_k^{-}-R_k^{\min }\right)\times <br><br>\underset{j=1,j\ne <br><br>k}{\overset{K}{\prod <br><br>}}<br><br>\left(R_j-R_j^{\min }\right),& \mathrm{Proportional}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{Fairness};<br><br>\\ \arg <br><br>\text{\hspace{1em}<br><br>}<br><br>{\max }_k<br><br>\left(R_k\right),& \mathrm{Reducing}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{maximal}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{rate};<br><br>\end{array}$

wherein R_k^min denotes a minimal requested data transmission rate for the k^th user.

8. The method of claim 1, wherein said pre-defined constraints include packet error rate, data transmission rates, and maximal allowed transmit power.

9. The method of claim 1, further comprising the step of:

performing a time-domain spreading with a pre-determined time-frequency code of a pre-determined length if said requested R_k is below a pre-determined data transmission rate value.

10. The method of claim 1, wherein said UWB system employs Orthogonal Frequency Division Multiplexing (OFDM) with said plurality of N sub-carriers modulated by the quadrature phase shift keying (QPSK), wherein at each OFDM symbol period, a modulated said OFDM symbol is transmitted over one of said S sub-bands in time-interleaved fashion across-said S sub-bands.

11. The method of claim 1, further comprising the step of:

defining a value range for each a_ks depending of the data transmission rate R_k of each k^th user from said plurality of K users.

12. The method-of claim 11, wherein

$a_{\mathrm{ks}}\in$

ϕ

⁡

( R k ) = { { 0 , 1 } , R k ≤

200 ⁢

 

⁢

Mbps ;

{ 0 , 1 , 2 } , R k >

200 ⁢

 

⁢

Mbps .

13. The method of claim 1, further comprising the step of:

assigning each sub-band from said plurality of S sub-band to a respective user of said plurality of K users at a transmission event to minimize a multiple access interference.

14. The method of claim 1, further comprising the step of:

defining a value range for each a_ks depending of the duration of a transmission block.

15. The method of claim 1, further comprising the steps of:

deriving an average signal-to-noise ratio (SNR) Γ

_k in accordance with

$\begin{array}{c}{\stackrel{\_}{\mathrm{\Gamma <br><br>}}}_k=<br><br>\underset{s=1}{\overset{S}{\sum <br><br>}}<br><br>a_{\mathrm{ks}}<br><br>P_k^s<br><br>F_k^s,\\ \mathrm{where}<br><br>\\ F_k^s<br><br>\stackrel{\mathrm{△<br><br>}}{=}<br><br><br><br>\frac{b_k}{N<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\sigma <br><br>}}_k^2}<br><br>\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br>G_k^s<br><br>\left(n\right)\end{array}$

wherein b_k is a constant depending on the k^th user transmission rate, G_k^s(n) is a channel gain and σ

_k² is a noise power at each subcarrier;

establishing a threshold value ε

for packet error rate (PER), and

maintaining said average SNR above a predetermined SNR threshold in accordance with

${\stackrel{\_}{\mathrm{\Gamma <br><br>}}}_k=\underset{s=1}{\overset{S}{\sum <br><br>}}<br><br>a_{\mathrm{ks}}<br><br>P_k^s<br><br>F_k^s\ge <br><br>\mathrm{\gamma <br><br>}<br><br>\left(\mathrm{\varepsilon <br><br>},R_k\right)$

to insure said PER is below said threshold value ε

.

16. A method for power controlled optimization of channel allocation in multi-band multi-user ultra-wideband (UWB) system for transmitting packets from a plurality of K users at a plurality of S sub-bands using a plurality of N sub-carriers, each k^th user requesting a data transmission rate R_k, the method comprising the steps of:

(a) defining a sub-band assignment matrix A, including a plurality of a_ks elements, wherein k=1, 2, . . . , K, and s=1, 2, . . . , S, and wherein each said a_ks element represents the duration of a data packet which a k^th user of said plurality of K users is allowed to transmit on the S^th sub-band of said plurality of S sub-bands,

(b) setting A=0<sub>K×

S</sub>,

(c) defining user optimization list K_live={1, 2, . . . , K};

(d) defining sub-band optimization list S_live={1, 2, . . . , S};

(e) calculating a dummy overall transmission power P_dummy^k for each k^th user of said plurality of k users, wherein P_dummy^k=min Σ

<sub>s−

1</sub>^Sa_ksP_k^s, sε

S_live;

(f) assigning said respective sub-band to a user k with the highest P_dummy^k, and removing said user k from said user optimization list K_live;

(g) removing said assigned respective sub-band from said sub-band optimization list S_live;

(h) repeating said steps (e)-(g) for the remaining users in said user optimization list K_live, until said K_live=0, thus assigning transmissions of said plurality of K users to the said plurality of S sub-bands in said sub-band optimization list S_live; and

(i) comparing a transmit power for each assigned sub-band to a pre-determined maximum power value.

17. The method of claim 16, further comprising the steps of:

indicating an outage if the transmit power for said each assigned sub-band is larger than said pre-determined maximum power value, or if S_live=0 and K_live≠

0; and

adapting said requested data transmission rate R_k.

18. The method of claim 17, further comprising the steps of:

(j) in said step of said requested data transmission rate R_k adaptation, choosing a single k^th user,

(k) reducing said single k^th user'"'"'s data transmission rate to a one-step reduced data transmission rate R_k, and repeating said steps (e)-(i); and

(l) repeating said steps (j)-(k) for remaining users in said plurality of K users.

19. The method of claim 17, further comprising the steps of:

choosing said single user in accordance with performance goals, including;

maximizing overall rate, or considering proportional fairness, or reducing maximal rate.

20. A multi-user multi-band ultra-wide band (UWB) system with an efficient sub-band assignment and power allocation, the UWB system transmitting data packets from a plurality of K users at a plurality of S sub-bands using a plurality of N sub-carriers using Orthogonal Frequency Division Multiplexing (OFDM), the system comprising:

a sub-band assignment matrix A, including a plurality of a_ks elements, wherein k=1, 2, . . . , K, and S=1, 2, . . . , S, and wherein each said a_ks element represents the duration of a data packet which a k^th user of said plurality of K users is allowed to transmit on the S^th sub-band and said plurality of S sub-bands,

a user optimization list K_live={1, 2, . . . , K};

a sub-band optimization list S_live={1, 2, . . . , S}; and

a processor unit adapted for;

(a) iterative calculation of a dummy overall transmission power P_dummy^k for each k^th user of said plurality of k users wherein P_dummy^k=min Σ

<sub>s−

1</sub>^Sa_ksP_k^s, s ε

S_live;

(b) assignment of said s^th sub-band to a user k with the highest P_dummy^k, and removal of said user k from said user optimization list K_live;

(c) removal of said assigned respective sub-band from said sub-band optimization list S_live;

(d) repetition of said steps (a)-(c) for remaining users in said user optimization list K_live, until said K_live=0, thus assigning transmissions of said plurality of the K users to said plurality of S sub-bands in said sub-band optimization list S_live; and

(e) comparison of a transmit power for each assigned sub-band to a pre-determined maximum power value;

said processor unit indicating an outage if the transmission power for said each assigned sub-band is larger than said pre-determined maximum power value or if S_live=0 and K_live≠

0; and

reducing said requested data transmission rate R_k for a chosen at least one user of said plurality of K users.