Dual carrier modulator for a multiband OFDM transceiver

• US 20050195765A1
• Filed: 01/21/2005
• Published: 09/08/2005
• Est. Priority Date: 03/08/2004
• Status: Active Grant

• Current Assignee: Intel Corporation
• Original Assignee: Infineon Technologies AG
• Inventors: Erlich, Yossi, Litsyn, Simon, Sharon, Eran
• Granted Patent: US 7,512,185 B2
• Time in Patent Office: Days
• US Class Current: 370/330
• CPC Class Codes: H04B 1/7176 Data mapping, e.g. modulation
• CPC Class Codes: H04L 27/3405 Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

Dual Carrier Modulator (DCM) for a Multiband OFDM (Orthogonal Frequency Division Multiplexing) Transceiver of a Ultra Wide Band (UWB) wireless personal access network transmitting OFDM modulated symbols,

• • wherein each OFDM symbol is modulated by a predetermined number (N_CBPS) of encoded bits,
  • said Dual Carrier Modulator (1) comprising:
    • (a) a grouping unit (1-1) for grouping N_CBPS encoded bits of a serial bit stream into bit groups each having a predetermined number (m) of bits;
    • (b) a mapping unit (1-2) for mapping each bit group received from said grouping unit to complex symbols (y) using an orthogonal transform; and
    • (c) a reordering unit (1-3) for reordering the complex symbols (y) mapped by said mapping unit, wherein each complex symbol (y) is provided to modulate a corresponding data tone of an OFDM symbol.

Claims

1. A dual carrier modulator (DCM) for a multiband orthogonal frequency division multiplexing (OFDM) transceiver of an ultra wide band (UWB) wireless network transmitting OFDM modulated symbols, wherein each OFDM symbol is modulated by a first predetermined number (N_CBPS) of encoded bits, said dual carrier modulator comprising:

(a) a grouping unit configured to group the N_CBPS encoded bits of a serial bit stream into bit groups each having a second predetermined number (m) of bits;

(b) a mapping unit configured to map each bit group received from said grouping unit to complex symbols (y); and

(c) a reordering unit configured to reorder the complex symbols (y) mapped by said mapping unit,

wherein each complex symbol (y) is provided to modulate a corresponding data tone of an OFDM symbol.

2. The dual carrier modulator of claim 1 wherein the first predetermined number is two hundred (N_CBPS=200) and the second predetermined number is four (m=4), such that the grouping unit groups two hundred encoded bits to bit groups each having four bits.

3. The dual carrier modulator of claim 2, wherein the mapping unit maps bit groups each having four bits respectively to two complex symbols (y_n;

y_n+NCBPS/4) to generate N_CBPS/2 complex symbols (y₀ . . . y_NCBPS/2) for modulating one N_CBPS/2 data tones of an OFDM symbol.

4. The dual carrier modulator of claim 3, wherein the mapping unit (1-2) comprises

a first mapping stage configured to map unipolar bit values of the encoded bits within each bit group to bipolar bit values and

a second mapping stage which provides an orthogonal 2×

2 mapping of two complex numbers composed of the four bipolar bits into two complex symbols.

5. The dual carrier modulator of claim 4, wherein the orthogonal 2×

2 mapping is defined by the equation

6. The dual carrier modulator of claim 5, wherein the mapping unit is formed by a look-up-table stored in a memory.

7. The dual carrier modulator of claim 6, wherein the look-up-table stored in said memory is given as follows:

8. The dual carrier modulator of claim 7, wherein the constant b is two (b=2).

9. The dual carrier modulator of claim 5, wherein the constant b is two (b=2).

10. A metric computation unit for a multiband orthogonal frequency division multiplexing (OFDM) transceiver of an ultra wide band (UWB) wireless network, said transceiver receiving OFDM symbols transmitted via a data transmission channel wherein each OFDM symbol is dual carrier modulated (DCM) by a predetermined number (N_CBPS) of encoded bits each modulating two data tones of the OFDM symbol, said metric computation unit comprising:

(a) a channel and noise estimation unit configured to estimate a channel response and a noise level for each data tone (n), or a group of adjacent tones, and calculate a corresponding estimated reception symbol (y(n));

(b) an equalizer operable to multiply each estimated reception symbol (y(n)) with an equalizer coefficient (eq(n)) in order to calculate for each data tone (n) a weighted reception symbol (w(n)=y(n)×

eq(n)); and

(c) a calculation unit configured to calculate for each bit transmitted via said data transmission channel a metric on the basis of weighted receptions symbols (w(n)) calculated by said equalizer for a group of data tones.

11. The metric computation unit of claim 10, wherein the calculation unit is configured to calculate, for each bit of a group of four bits modulating two data tones of an OFDM symbol transmitted via said data transmission channel, a log-likelihood ratio (LLR) estimation as a metric on the basis of the weighted reception symbols (w(n)) calculated by the equalizer for said two data tones.

12. The metric computation unit of claim 10, wherein the channel and noise estimation unit is configured to estimate the channel response (h) and a noise variance (v(n)) for each data tone during a preamble phase on the basis of a predetermined preamble signal.

13. The metric computation unit of claim 10, wherein the estimated reception symbols (y(n)), the equalizer coefficients (eq(n)) and the weighted reception symbols (w(n)) are complex.

14. The metric computation unit of claim 12, wherein the equalizer coefficients (eq) of said equalizer are selected during the preamble phase for each data tone as follows:

eq(n)=2 h*(n)/v(n)

wherein v(n) is an estimated noise level of said data tone, and

h*(n) is the conjugate of the channel response h(n) of said data tone n.

15. The metric computation unit of claim 12, wherein for each data tone the following values are computed:

p(n)=h(n)•

h*(n)/v(n).

16. The metric computation unit of claim 15 wherein for each pair of tones n₁, n₂ used to modulate four bits, the following real value is computed:

dp(n₁,n₂)=4•

b•

[p(n₁)−

p(n₂)].

17. The metric computation unit of claim 10 wherein a data-rate-dependent noise variance is assumed.

18. The metric computation unit of claim 11 wherein the calculation unit is configured to calculate the log-likelihood ratios (LLR) of said group of four bits on the basis of the weighted complex reception symbols (w(n₁), w(n₂)) for two data tones (n₁, n₂) as follows:

dw_r=2[b•

w_r,1−

w_r,2]
sw_r=2[w_r,1+b•

w_r,2]
q_r=2(1+b)•

w_r,1+2(b−

1)•

w_r,2
dw_i=2[b•

w_i,1−

w_i,2]
sw_i=3[w_i,1−

wi,2]
q_i=2(1+b)•

w_i,1+2(b−

1)•

w_i,2
dp=4•

b•

[p(n₁)−

p(n₂)]
LLR(bit#1)=q_r+log {1+exp(dp−

dw_r)}−

log {1+exp(dp+dw_r)}
LLR(bit#2)=q_r+log {1+exp(dp−

sw_r)}−

log {1+exp(dp+sw_r)}
LLR(bit#3)=q_i+log {1+exp(dp−

dw_i)}−

log {1+exp(dp+dw_i)}
LLR(bit#4)=q_i+log {1+exp(dp−

sw_i)}−

log {1+exp(dp+sw_i)}

where w_r,n is the real part of w(n) and w_i,n is the imaginary part of w(n).

19. The metric computation unit according to claim 18 wherein the function log {1+exp(x)} is realized by a look-up table.

20. The metric computation unit according to claim 18 wherein the function log {1+exp(x)} is approximated by: