MXPA06011072A - Apparatus for reducing channel interference between proximate wireless communication units - Google Patents

Abstract

Apparatus for reducing adjacent channel interference between proximate wireless communication units. Each wireless communication unit includes a digital baseband circuit and an analog baseband circuit. The digital baseband circuit includes at least one group delay compensation equalizer and at least one finite-impulse response (FIR) filter. The analog baseband circuit includes a radio (transmitter section), a power amplifier and a narrowband filter. The narrowband filter compensates for deficiencies of the power amplifier including distortion and radio frequency (RF) power spill over. The group delay compensation filter compensates for undesired characteristics (e.g., group delay variation)exhibited by the narrowband filter.

Description

APPARATUS TO REDUCE CHANNEL INTERFERENCE BETWEEN NEXT WIRELESS COMMUNICATION UNITS FIELD OF THE INVENTION The present invention relates to a wireless communication that includes a plurality of wireless communication units, (ie, mobile stations, base stations or the like). More particularly, the present invention relates to an apparatus for reducing channel interference between said wireless communication units that are close to each other.

BACKGROUND Conventional wireless communication systems include a plurality of wireless communication units that communicate through a wireless medium. Said wireless communication units may include wireless transmission / reception units (WTRUs), (ie, mobile stations), base stations, or the like. When two or more wireless communication units are close to each other while operating in frequency bands that are adjacent or separated by only some channel bandwidths, a problem known as "adjacent channel interference". The receiver of a wireless communication unit may be limited with respect to interference by spectral emissions from the transmitter in another wireless communication unit nearby, unless the transmitted spectral content is sufficiently suppressed to have no effect on the reception of the adjacent operator. Interference mitigation is required, but it is not always practical. Figure IA shows an ideal output spectrum generated by multiple wireless communication units operating in adjacent bands. Figure IB shows a realistic scenario output spectrum of multiple wireless communication units operating in adjacent bands. In the ideal output spectrum of Figure 1A, there is no spectral energy that leaks into adjacent bands. In the realistic output spectrum of Figure IB, the spectral energy leaks into the adjacent bands due to the non-linearities in the transmitter of the wireless communication units, mostly due to a power amplifier (PA) therein. These non-linearities cause the spectral re-growth in the adjacent bands, thus limiting the frequency spacing between the wireless communication units. The problem of adjacent channel interference can be minimized with the use of linearized radio frequency (RF) PAs. Various known types of distortion correction techniques can be used in conjunction with the PAs for reduce nonlinearities and minimize spectral re-growth within adjacent channels. However, these corrected APs have some disadvantages since corrected APs tend to be very expensive, are highly unstable for long periods, have poor power aggregate efficiency, and the performance of the spectral re-growth correction is degraded with signals from impulses. Also, such corrected PAs almost always need to be built according to custom. The linearized PAs also have the capacity to correct limited spectral re-growth, which is less than that required by the specifications of the Universal Mobile Telecommunications System (UMTS). In conventional wireless communication systems, different types of amplifiers are used to provide reduced levels of interference, such as preamplification systems, adaptive or non-adaptive pre-distortion amplification systems, feedback amplification systems, and large amplifiers. Class A power oversized. However, said amplifiers have characteristics of power overflow and distortion that are not convenient. A method and apparatus for reducing channel interference between nearby wireless communication units and for eliminating the aforementioned undesirable features of the amplifiers of the present invention is convenient. power.

THE INVENTION The present invention relates to an apparatus for reducing adjacent channel interference between nearby wireless communication units. Each wireless communication unit includes a digital baseband circuit and an analog baseband circuit. The digital baseband circuit includes at least one group delay compensation equalizer and at least one finite impulse response (FIR) filter. The analog baseband circuit includes a radio (transmitter section), a power amplifier and a narrow band filter. The narrow band filter compensates for power amplifier deficiencies, which include radio frequency (RF) distortion and overflow. The group delay compensation filter compensates for undesirable characteristics (eg, group delay variation), presented by the narrow band filter.

BRIEF DESCRIPTION OF THE DRAWINGS A more detailed understanding of the invention can be obtained from the following description of a preferred embodiment, given by way of example and to be understood together with the accompanying drawings, wherein: Figure 1A shows an output spectrum ideal generated by multiple wireless communication units operating in adjacent bands; Figure IB shows a realistic scenario output spectrum of multiple wireless communication units operating in adjacent bands; Figure 2 shows a block diagram of a wireless communication unit configured to reduce adjacent channel interference, in accordance with the present invention; and Figure 3 shows an example of a group delay compensation equalizer used in the wireless communication unit of Figure 2.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Although the characteristics and elements of the present invention are described in the preferred embodiments, in particular combinations, each characteristic or element can be used alone (without the other characteristics and elements of the preferred embodiments) or in various combinations with or without the other features and elements of the present invention. The present invention is applicable to any type of conventional wireless communication system that includes systems using time division duplex (TDD), frequency division duplex (FDD), multiple access by code division (CDMA), CDMA 2000, synchronous CDMA by time division (TDSCDMA), orthogonal frequency division multiplexing (OFDM) or similar. Next, the expression "wireless communication unit" includes, but is not limited to, a wireless transmission / reception unit (WTRU), a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a base station, a Node B, a site controller, an access point or any other type of interface device capable of operating in a wireless environment. The features of the present invention can be incorporated in an integrated circuit (IC) or be configured in a circuit comprising a large number of interconnected components. The present invention relates to a wireless communication unit configuration that yields significantly lower RF power overflow and distortion. Figure 2 shows a block diagram of a wireless communication unit 200 configured to reduce adjacent channel interference, in accordance with the present invention. The wireless communication unit 200 includes a modem 205 that outputs signal components in phase (I or real or "Re") or quadrature (Q or imaginary or "Im"), compensation equalizers group delay 210A and 210B, finite impulse response (FIR) filters 215A and 215B, digital to analog (D / A) converters 220A and 220B, one radio (transmitter section) 225, an RF RF 230, a high-quality narrow band ("Q") 235 cavity filter and an antenna 240. The modem 205 'contains the baseband processing used to generate digital baseband symbols or chips in the wireless communication unit 200. The group delay compensation equalizers 210A, 210B correct the very large group delay variations caused by the high narrow band cavity filter Q 235. This will allow compliance of wireless based communication units in TDD UMTS regarding co-location or specifications of the same geography. Both equalizers 210A and 210B may be configured as an FIR filter. Alternatively, both equalizers 210A and 210B can be configured as an infinite impulse response filter (IIR) implementation. • Both equalizers 210A and 210B and the FIR filters 215A and 215B include delay lines with leads. FIR filters 215 shape the chips generated by modem 205. FIR filters can be square-root cosine (RRC) filters. The D / A converters convert the digital baseband signal into an analog baseband signal, which the radio 225 modulates then on a carrier. The wireless communication unit of Figure 2 includes a transmitter that incorporates group delay equalization in the baseband portion of the transmitter and a high-band narrowband cavity filter Q 235 in the RF portion of the transmitter. These components together provide a high adjacent channel leak (ACLR) rejection and an alternate channel rejection in all transmission applications that require high adjacent and alternating channel leakage rejection levels. In an exemplary application for TDM UMTS, the pass band of the cavity filter 235 is 5 MHz, although this technique can be extended to other standards. The high Q 235 narrowband cavity filter provides high leak rejection in adjacent and alternating channels, at the expense of creating a wide group delay variation within the bandwidth of interest. This wide group delay variation degrades the signal integrity of the signal received at the receiving end of the communication system, thus rendering this technique undesirable unless the group delay variation is compensated. The group delay compensation equalizers 210A, 210B reduce the group delay variation caused by the high narrow band cavity filter Q 235, convolving a group delay characteristic which is the inverse of the group delay characteristic of the cavity filter narrow band of high Q 235. This causes a semi-flat group delay response across the band of interest, thus allowing the use of the high-band narrow Q 235 cavity filter to achieve an adjacent channel leak rejection high.' Next, Table 1 provides some examples of the combination of several types of basic Class A linear PAs, linearized PAs using anticipation, feedback, or pre-distortion type linearization techniques, and high Q narrow band cavity filters. together. Table 1 describes the requirements for adjacent channel leak rejection throughout the entire path of the transmitter. The input ACLR is presented at the input of the D / A converters 22OA and 220B. Columns five (Impr ACLR PA Lin) and six (Impr ACLR Filter) describe the improvement of ACLR of the linearized PA and narrow band filter of high Q, respectively. Column seven (total ACLR) provides the total accumulated ACLR of the transmitter path.

Table1: Cavity Filter Configurations Narrow High Q Band and Power Amplifier Case I of Table 1 shows the improvement of ACLR using only a linearized power amplifier. Case II of Table 1 shows that, using a four-section high-Q narrow band cavity filter, the same ACLR can be achieved, while relaxing the transmitter path requirements before the PA stage and the ACLR input inside the D / A converters, while using a basic class A power amplifier. Case III of Table 1 is similar to Case II, with the exception that a high-Q narrow band cavity filter of eight sections is used. Cases IV and V of Table 1 are high ACLR configurations using a linearized PA with narrow-band high-Q cavity filters of four and eight sections, respectively. Figure 3 shows an example of how the group delay compensation equalizers 210A and 210B used in the wireless communication unit of Figure 2 are configured. Each of the equalizers 210 includes a delay line with taps 305 that is weighted by a plurality of coefficients b0í b! , ..., bn, so that the combined group delay of the equalizers 210 and the narrowband cavity filter 235 present a minimum residual group delay variation, (ie residual ripple). The objective response used in the generation of the coefficients of the equalizers 210 is the inverse of the group delay variation of the narrow band cavity filter '235. There are various ways of generating the coefficients based on the target response, which is extend beyond the scope of the present invention. In one embodiment, the group delay compensation filter 210A and the FIR filter 215A may be combined in a first single unit, and the group delay compensation filter 210B and the FIR filter 215B may be combined in a second single unit. Thus, the coefficients of the equalizers 210 are convolved with the FIR filters 215 in each respective combination to produce a large number of coefficients that perform the functions of both the equalizers 210 and the filters 215. In another embodiment, an RF PA is used. corrected or linearized instead of a standard RF Power Amplifier. This embodiment of the present invention will obtain better operation. In some scenarios, a commercially-acquired corrected power amplifier can produce an improvement of between 25 dB and 30 dB for adjacent channel power emissions through an uncorrected amplifier of the same size. Using the apparatus of this invention instead from . A corrected amplifier purchased commercially, an improvement of between 60 dB and 80 dB is possible for less than the cost of the corrected amplifier approach. This operating gain can be achieved without incurring additional distortion that could otherwise create large group delay variations. There are some TDD / FDD co-location scenarios that need to implement the present invention to fully comply with the UMTS specifications. Although the features and elements of the present invention are described in the preferred embodiments, in particular combinations, each characteristic or element can be used alone (without the other features and elements of the preferred embodiments) or in various combinations with or without other features and elements of the present invention. While the specific embodiments of the present invention have been shown and described, a large number of modifications and variants could be made by one skilled in the art, without departing from the scope of the invention. The foregoing description serves to illustrate and not limit the particular invention in any way.

Claims (22)

1. CLAIMS 1. A wireless communication unit characterized in that it comprises: (a) a digital baseband circuit comprising at least one group delay compensation equalizer and at least one finite impulse response (FIR) filter; and (b) an analog baseband circuit comprising a radio, a power amplifier and a narrow band filter, where the narrow band filter compensates for the deficiencies presented by the power amplifier, and the compensation filter compensates for the characteristics not convenient presented by the narrow band filter.
2. 2. Wireless communication unit according to claim 1, characterized in that the narrow band filter is a high quality narrow band (Q) cavity filter that provides a high adjacent channel leak rejection in adjacent channels and creates a broad group delay variation over the convenient pass band.
3. 3. Wireless communication unit according to claim 2, characterized in that the group delay compensation equalizer substantially reduces the variation of group delay caused by the high-Q narrow band cavity filter, convolving with an inverse of the group delay characteristic of the high Q narrow band cavity filter, which results in a more convenient group delay response across the step band.
4. 4. Wireless communication unit according to claim 2, characterized in that the passband is 5 MHz.
5. 5. Wireless communication unit according to claim 1, further characterized in that it comprises at least one digital to analog converter. (D / A) that connects the digital baseband circuit with the analog baseband circuit.
6. 6. Wireless communication unit according to claim 1, characterized in that the group delay compensation equalizer includes a delay line with taps weighted by a plurality of coefficients, so that the output of the delay compensation equalizer of group is substantially equivalent to the inverse of the group delay variation created by the narrow band cavity filter.
7. 7. Wireless communication unit according to claim 1, characterized in that the power amplifier is a linear power amplifier of class A.
8. 8. Wireless communication unit according to claim 1, characterized in that the power amplifier is a linearized power amplifier that uses linearization techniques such as anticipation, realization or pre-distortion.
9. 9. Wireless communication unit according to claim 1, characterized in that the wireless communication unit is a base station.
10. 10. Wireless communication unit according to claim 1, characterized in that the wireless communication unit is a wireless transmission / reception unit (WTRU).
11. 11. Wireless communication unit according to claim 1, characterized in that the deficiencies of the power amplifier compensated by the narrow band filter include distortion and overflow of radio frequency (RF) power.
12. 12. Integrated circuit (IC) characterized in that it comprises: (a) digital baseband circuit comprising at least one group delay compensation equalizer and at least one finite impulse response (FIR) filter; and (b) analog baseband circuit comprising a radio, a power amplifier and a narrow band filter, where the narrow band filter compensates for the deficiencies presented by the power amplifier, and the compensation filter compensates for the characteristics not conveniently presented by the narrow band filter.
13. 13. IC according to claim 12, characterized in that the narrow band filter is a high quality narrow band cavity filter (Q) that provides a high adjacent channel leak rejection in adjacent channels and creates a broad group delay variation over a convenient passband.
14. 14. IC according to claim 13, characterized in that the group delay compensation equalizer • substantially reduces the group delay variation caused by the high-Q narrowband cavity filter convolving with an inverse of the delay characteristic. of the high-Q narrow band cavity filter group, which results in a more convenient group delay response across the passband. •fifteen.
15. IC according to claim 13, characterized in that the passband is 5 MHz.
16. 16. IC according to claim 12, further characterized in that it comprises, at least one digital to analog converter (D / A) that connects the digital baseband circuit with the analog baseband circuit.
17. 17. IC according to claim 12, characterized in that the group delay compensation equalizer includes a delay line with taps weighted by a plurality of coefficients, so that the output of the group delay compensation equalizer is substantially equivalent inverse of the group delay variation created by the narrowband cavity filter. '
18. 18. IC according to claim 12, characterized in that the power amplifier is a class A linear power amplifier.
19. 19. IC according to claim 12, characterized in that the power amplifier is a linearized power amplifier that uses linearization of type anticipation, feedback or pre-distortion.
20. IC in accordance with claim 12, characterized in that the IC is comprised of a base station.
21. 21. IC according to claim 12, characterized in that the IC is comprised by a wireless transmission / reception unit (WTRU).
22. 22. IC according to claim 12, characterized in that the deficiencies of the power amplifier compensated by the narrow band filter include distortion and overflow of radio frequency (RF) power. RESUME Apparatus for reducing adjacent channel interference between nearby wireless communication units. Each wireless communication unit includes a digital baseband circuit and analog baseband circuit. The digital baseband circuit includes at least one group delay compensation equalizer and at least one finite impulse response (FIR) filter. The analog baseband circuit includes a radio (transmitter section), a power amplifier and a narrow band filter. The narrowband filter compensates for power amplifier deficiencies that include radio frequency (RF) power distortion and overflow. The group delay compensation filter compensates for undesirable characteristics (eg, group delay variation) presented by the narrow band filter.