Wireless device and method for interference and channel adaptation in an OFDM communication system

#The present invention pertains to wireless communications, and in particular to orthogonal frequency division multiplexed communications.

#Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technique that uses orthogonal subcarriers to transmit information within an available spectrum. Because the subcarriers are orthogonal to one another, they may be spaced much more closely together within the available spectrum than, for example, the individual channels in a conventional frequency division multiplexing (FDM) system. An OFDM system may achieve orthogonality by using subcarriers that have a null at the center frequency of the other subcarriers. The orthogonality of the subcarriers may help prevent inter-subcarrier interference within the system. Before transmission, the subcarriers may be modulated with a low rate data stream. The transmitted symbol rate of the OFDM system is low, and thus the transmitted OFDM signal may be highly tolerant to multipath delay spread within the channel. For this reason, many modem digital communication systems are turning to OFDM as a modulation scheme for signals that need to survive in environments having multipath reflections and/or strong interference. Many wireless communication standards have already adopted OFDM including, for example, the IEEE 802.11a standard, the Digital Video Broadcasting Terrestrial (DVB-T) broadcasting standard, and the High performance radio Local Area Network (HiperLAN) standard. In addition, several industry consortia, including the Broadband Wireless Internet Forum and the OFDM Forum, are proposing OFDM for fixed wireless access systems.

#One problem with conventional OFDM systems is that it is difficult to make efficient use of the channel due to in-band interference and channel effects (e.g., multipath reflections/frequency selective fading). These dynamically changing channel characteristics, for example, reduce the number of bits per symbol that can be effectively communicated. Conventional OFDM systems use equalization schemes to compensate for channel effects by applying equalization coefficients to the received signal to improve the likelihood of accurate detection. Although conventional equalization schemes may allow an OFDM channel to operate at a higher data rate, they do not allow an OFDM channel to reach its “water-filling capacity” because they do not take into account channel conditions on a per subcarrier basis. Furthermore, conventional OFDM equalization schemes do not take into account channel conditions, such as in-band interference, in only portions of the channel bandwidth.

#The appended claims are directed to some of the various embodiments of the present invention. However, the detailed description presents a more complete understanding of the present invention when considered in connection with the figures, wherein like reference numbers refer to similar items throughout the figures and:

#FIG. 1 is a wireless communication environment illustrating the operation of an embodiment of the present invention;

#FIG. 2 is a highly simplified functional block diagram of a wireless communication device in accordance with an embodiment of the present invention;

#The following description and the drawings illustrate specific embodiments of the invention sufficiently to enable those skilled in the art to practice it. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The scope of the invention encompasses the full ambit of the claims and all available equivalents.

#FIG. 1 is a wireless communication environment illustrating the operation of an embodiment of the present invention. Communication environment 100 includes one or more wireless communication devices (WCD) 102 which may communicate with access point (AP) 104 over communication bi-directional OFDM links 110. WCDs 102 may include, for example, personal digital assistants (PDAs), laptop and portable commuters with wireless communication capability, web tablets, wireless telephones, wireless headsets, pagers, instant messaging devices, MP3 players, digital cameras, and other devices that may receive and/or transmit information wirelessly. WCDs 102 may communicate with AP 104 using a multi-carrier transmission technique, such as an orthogonal frequency division multiplexing (OFDM) technique, that uses orthogonal subcarriers to transmit information within an assigned spectrum. WCDs 102 and AP 104 may also implement one or more communication standards, such as the IEEE 802.11a standard, the Digital Video Broadcasting Terrestrial (DVB-T) broadcasting standard, and the High performance radio Local Area Network (HiperLAN) standard.

#In addition to facilitating communications between WCDs 102, in one embodiment AP 104 may be coupled with one or more networks, such as an intranet or the Internet, allowing WCDs 102 to access such networks. For convenience, the term downstream is used herein to designate communications in the direction from AP 104 to WCDs 102 while the term upstream is used herein to designate communications in the direction from WCDs 102 to AP 104, however, the terms downstream and upstream may be interchanged. In one embodiment, upstream and downstream communications may be time division multiplexed (TDM), although this is not a requirement. In another embodiment, downstream communications may be broadcast to more than one of WCDs 102 and may be frequency division multiplexed (FDM). WCDs 102 may support duplex communications utilizing different spectrum for upstream and downstream communications, although this is not a requirement. In one embodiment, upstream and downstream communications may share the same spectrum for communicating in both the upstream and downstream directions. Although FIG. 1 illustrates point-to-multipoint communications, embodiments of the present invention are suitable to both point-to-multipoint and point-to-point communications.