Joint channel and noise variance estimation in a wideband OFDM system
AssigneeKoninklijke Philips Electronics N.V.
InventorsMonisha Ghosh, Vasanth Gaddam
Life of this patent
Estimating the term…
Abstract
A method and system for use in a wireless-local-area network (WLAN), for simultaneously estimating the unknown multi-path channel and noise characteristics and using the channel and noise estimates to improve system performance in the presence of narrowband interferers. Estimates are made for the unknown multi-path channel and noise characteristic without a-priori knowledge of the location of the interference in the band and this information is used to generate soft-metrics for a Viterbi decoder. By using the improved channel and noise estimates, the packet error rate (PER) of an 802.11g WLAN system may be maintained despite collisions with interfering packets thereby allowing the 802.11g system to be less sensitive to the interference.
Claims16
In a wireless local area network (WLAN), a method for estimating an unknown multi-path channel and a noise variance in the presence of narrowband interference, said method comprising the steps of:
- (a) receiving a time domain OFDM data packet;
- (b) converting said time domain OFDM data packet to a frequency domain OFDM data packet;
- (c) extracting a vector of training symbols having known transmitted values from said frequency domain OFDM data packet;
- (d) using said training symbols to derive a simplified channel estimate that assumes no interference is present in the unknown multi-path channel, and
- (e) estimating a noise variance of said narrowband interference using said simplified channel estimate at said step (d).
In a wireless local area network (WLAN), a method for estimating an unknown multi-path channel and a noise variance in the presence of narrowband interference, said method comprising the steps of:
- (a) receiving a time domain OFMD data packet;
- (b) converting said time domain OFDM data packet from said time domain to a frequency domain OFDM data packet;
- (c) using training symbols from long training sequences L1 and L2 contained within said OFDM data packet to derive a simplified channel estimate in frequency as:
- HLS=F(GHG)−1GHr
- where F and A and G=AF are matrix values which are all known a-priori for said long training sequences L1 and L2 at a receiving node in said WLAN;
- (d) estimating a noise variance of said narrowband interference using said simplified channel estimate at said step (a), comprising the steps of:
- (1) computing an error vector e as:
- e=r−AĤLS;
- and
- (2) calculating said noise variance estimate as:
- σk2=|ek|2;
- (e) estimating a transmitted symbol as
- ak,I=rk,I/Ĥk
- (f) slicing said estimated transmitted symbol ak,I to the nearest constellation point;
- (g) estimating the noise variance at frequency k as:
- {circumflex over (σ)}k,i2=|rk,i−Ĥkâk,i|2
- (h) averaging the noise variance estimate over N OFDM data frames to obtain a more refined noise variance estimate as:
- σ
- ^
- k
- 2
- =
- 1
- N
- f
- +
- 1
-
- ∑
- i
- =
- 0
- Nj
-
-
- σ
- ^
- k
- ,
- i
- 2
-
- k
- =
- 1
- n
-
-
- …
-
- ,
- N
- .
In a wireless local area network (WLAN), a system for estimating an unknown multi-path channel and a noise variance in the presence of narrowband interference, said system comprising:
- means for receiving a time domain OFDM data packet;
- means for converting said time domain OFDM data packet to a frequency domain OFDM data packet;
- means for extracting a vector of training symbols having known transmitted values from said frequency domain OFDM data packet;
- means for using said training symbols to derive a simplified channel estimate that assumes no interference in said unknown multi-path channel;
- and
- means for estimating a noise variance of said narrowband interference using said simplified channel estimate at said step (d).
In a wireless local area network (WLAN), a system for estimating an unknown multi-path channel and a noise variance in the presence of narrowband interference, said system comprising:
- mean for receiving a time domain OFMD data packet;
- means for converting said time domain OFDM data packet from said time domain to a frequency domain OFDM data packet;
- means for using training symbols from long training sequences L1 and L2 contained within said OFDM data packet to derive a simplified channel estimate in frequency as:
- HLS=F(GHG)−1GHr,
- where F and A and G=AF are matrix values which are all known a-priori for said long training sequences L1 and L2 at a receiving node in said WLAN;
- means for estimating a noise variance of said narrowband interference using said simplified channel estimate at said step (a), comprising the steps of:
- (1) computing an error vector e as:
- e=r−AHLS;
- and
- (2) calculating said noise variance estimate as:
- σk2=|ek|2;
- means for estimating a transmitted symbol as
- ak,I=rk,I/Ĥk
- means for slicing said estimated transmitted symbol ak,I to the nearest constellation point;
- means for estimating the noise variance at frequency k as:
- {circumflex over (σ)}k,i2=|rk,i−Ĥkâk,i|2
- means for averaging the noise variance estimate over N OFDM data frames to obtain a more refined noise variance estimate as:
- σ
- ^
- k
- 2
- =
- 1
- N
- f
- +
- 1
-
- ∑
- i
- =
- 0
- Nj
-
-
- σ
- ^
- k
- ,
- i
- 2
-
- k
- =
- 1
- n
-
-
- …
-
- ,
- N
- .
Dependencies are inferred from the claim text.