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METHOD AND APPARATUS FOR PROCESSING COMMUNICATION SERVICES
MULTIPLE WIRELESS
FIELD OF THE INVENTION The present invention relates to wireless communication systems. More particularly, the present invention relates to a method and apparatus for processing multiple wireless communication services in a receiver.
BACKGROUND Program-defined radio (software) (SDR) is a scheme in which multiple wireless communication standards are supported in a wireless transmitter / receiver unit (WTRU) and radio frequency (RF) signals are processed by units defined by program (software) with SDR, a single physical hardware platform can support multiple wireless communication standards without replacing physical element components, and downloaded programs can reconfigure physical elements. In this way the WTRU can be configured quickly to support newly developed wireless communication protocols and standards. Typical single-mode cellular base stations and WTRUs include an analog front end of a heterodyne radio receiver, an analog-to-digital converter (ADC) of fixed sample rate and subsequent digital processing units. At the analog front end, the desired signal is filtered and then reduced to a fixed intermediate frequency (IF) band. The ADC operates at a fixed sampling rate that is selected a priori, based on the bandwidth of the desired signal requirements of the demodulation algorithms of the digital procedure and other factors. Currently, WTRUs are configured to process multiple services received through multiple channels. For example, a WTRU can support communications in both a digital cellular system (DSC) and a broadband code division multiple access (WCDMA) system. Each service is processed through a corresponding receiving path in the WTRU and is entered separately within a modem through a corresponding receiving path in the WTRU and is entered separately in a modem in the WTRU for processing. However, only one service is supported at a given moment in each receiving path. Current WTRU designs also include front end configurations that involve a switch or a multiplexer and multiple filters that separate the signals into different receiver paths for the frequency band of each service. When the base station or WTRU is supporting multiple simultaneous services and / or channels on different carrier frequencies in a single radio receiver, the various services or channels are separately filtered and reduced at the analog front end to IF and then converted separately. to digital samples at fixed sampling rates. The ADC sampling rate is one of the factors that affects the power consumption of the receiver. The power consumption of the ADC and other processing blocks in a modem, in general is proportional to the sampling rate, higher sampling rates require more power than lower sample rates. Therefore, the prior art WTRUs require extensive resources of physical elements to support multiple services and the configuration is not desirable in terms of battery life of the WTRU.
BRIEF DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for processing multiple wireless communication services in a receiver. In accordance with the present invention, more than one wireless communication service is received and processed simultaneously. The services - are transmitted via different carrier frequency bands and the received carrier frequency bands are reduced to an intermediate frequency (IF) band. Local oscillator (LO) frequencies are established so that the reduced IF bands of the multiple services are within a single IF band. In an alternative modality, the defined program radius (SDR) is implemented using an ADC and adaptively selects the sampling frequency for analog-to-digital conversion of a plurality of input signals comprising two or more services received in two or more different frequency bands and adaptively select LO frequencies. Each input signal carries a different service via different frequency bands. The input signals are received simultaneously. Each service is subject to a minimum signal-to-noise and distortion (SINAD) requirement. The input signals are converted to IF band signals by mixing the input signals with multiple LO signals at certain frequencies. The LO frequencies are selected in an adaptive manner so that the IF bands are spectrally adjacent or overlap with each other to some degree. The SINAD of the services is measured in each of a plurality of spectral superposition conditions. The LO frequencies and the sampling frequency are then adjusted based on the SINAD measurement results. The process is preferably repeated continuously.
BRIEF DESCRIPTION OF THE DRAWINGS A more detailed understanding of the invention can be obtained from the following description of the preferred embodiments, which are provided by way of example so that they are understood together with the accompanying drawings, in which: Figure 1 is a block diagram of a receiver, according to a first embodiment of the present invention; Figures 2A-2D are signal spectrum diagrams in each stage in the receiver of Figure 1; Figure 3 is a block diagram of a receiver, according to a second embodiment of the present invention; Figures 4-4D are signal spectrum diagrams in each stage in the receiver of Figure 3; Figure 5 is a block diagram of a receiver according to a third embodiment of the present invention; Figures 6A-6D are signal spectrum diagrams in each stage in the receiver of Figure 5;
Figure 7 is a block diagram of a look-up table (LUT) used to implement adaptive frequency reduction conversions, in accordance with the present invention; Figure 8 is a block diagram for synthesizing frequencies for local oscillators, according to the present invention; Figure 9 is a flow chart of a method for simultaneously processing multiple wireless communication services in a receiver, in accordance with the present invention; Figure 10 is a block diagram of a receiver for adaptively selecting the sampling frequency for an analog-to-digital conversion of two input signals, in accordance with the present invention; Figures 11A-11F are block diagrams illustrating the frequency shift of RF bands at the final IF frequencies, according to the present invention; and Figure 12 is a flow chart of a method for adaptively selecting the sampling frequency for analog-to-digital conversion of a plurality of signals input to a receiver according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Hereinafter, the terminology "WTRU" includes but is not limited to a user equipment, a mobile station, a fixed or mobile subscriber unit, a pager or any other type of device capable of operating in a wireless environment. With reference to the following, the terminology "base station" includes but is not limited to a B-node, a site controller, an access point or any other type of interconnection device in a wireless environment. The features of the present invention can be incorporated into an integrated circuit (IC) or they can be configured in a circuit comprising a multitude of interconnecting components. The present invention provides a method and apparatus for use in support of simultaneous reception of multiple wireless communication services in a single receiver chain. The physical elements can be configured by the program. In the following, the present invention will be explained with reference to DSC and frequency division duplex WCDMA (FDD) as examples of simultaneous services. However, it should be noted that the present invention is applicable to any other service and any number of simultaneous services. The numerical values shown in the drawings are provided as an example, not as a limitation, and any other numerical value may be implemented without thereby departing from the teachings of the present invention. Figure 1 is a block diagram of a receiver 100 according to a first embodiment of the present invention. Figures 2A-2D are signal spectrum diagrams in each stage of the receiver 100 of Figure 1. A diplexer 102 and a circulator 104 limit the band of the input spectrum, which is shown in Figure 2A and combines the descending bands of desired service, while minimizing component losses before a low noise amplifier (LNA) 106. This also establishes a quantity of system noise which mainly comprises the noise amount of the LNA 106 plus any loss before the LNA 106, insofar as the LNA 106 has a sufficient gain (10-15 dB) to minimize the contributions of noise quantities of the second stage of the rest of the receiver chain. The diplexer 102 removes any intermediate rising band (such as the rising band FDD, in FIG. 2A) which lies between the desired descending bands and therefore avoids saturation of the broadband LNA 106. The arbitrary channels in two full reception bands can be received simultaneously and the service selection is configurable by program. The band-limited input spectrum is amplified by the LNA 106 and filtered by a first filter 108. The input spectrum after being filtered by the first filter 108 is shown in Figure 2B. The band-limited input signal is reduced to a first IF bandwidth by a mixer 110 with a fixed frequency LO1. The first IF is filtered again by a second filter 112 to eliminate image frequencies and blockers; and then amplified by a variable gain amplifier 114 (VGA). The first IF spectrum, as output by VGA 114 is shown in Figure 2C. By using image frequency shifts, a second reduction conversion is carried out by a mixer 116 with L02. The second IF spectrum is shown in Figure 2D. The frequency L02 is set so that the second reduction conversion causes the multiple service downlink bands to be folded into a second IF bandwidth, as shown in Figure 2D. The downlink band DSC and the downlink band FDD of WCDMA are folded into a second bandwidth IF. This allows the use of high Q filters to attenuate out-of-band blockers and interference in the second IF bandwidth. Multiple LO frequencies can also be used to place the multiple service downlink bands anywhere within a second defined IF bandwidth. The receiver 100 of FIG. 1 performs two reduction conversions. However, it should be noted that the configuration of the receiver 100 in FIG. 1 and other embodiments of the present invention which will be explained later, are merely preferable embodiments of the present invention and one or more of two downconverting can be implemented. The local oscillators, LO1 and L02 are established using an adaptive frequency plan with the fixed filters to bend the receiver downlink bands to a second IF while minimizing the second IF bandwidth. The final IF signals are sampled in a descending and additional manner by an analog-to-digital converter (ADC) 124 after being processed by filter 118, 122 and a VGA 120. By minimizing the second IF bandwidth, the sampling frequency of ADC 124 can be adaptive and in this way the energy consumption of the final digital decay conversion to the baseband is minimized. The final IF bandwidth depends on the receiver's signal-to-noise and distortion (SINAD) ratio measurement. The SINAD measurement includes the distortion products that are within the processing bandwidth of the receiver. Normally, only one signal with this bandwidth is present and the distortion products are not generated, so that only the signal to noise ratio (SNR) measurement is required. Since there are multiple signals present in the receiver, the distortion products are generated within the processing band and these levels need to be considered in the SNR measurement. In accordance with the present invention, the minimum bandwidth is selected when the highest SINAD is measured, and conversely the largest final bandwidth is selected when the lowest SINAD is measured. Figure 3 is a block diagram of a receiver 200 according to a second embodiment of the present invention. Figures 4A-4D are signal spectrum diagrams in each stage in the receiver of Figure 3. A diplexer 202 and a band limit circulator 204 of the input spectrum, which is shown in Figure 4A. The band-limited input spectrum is amplified by an LNA 206 and filtered by a first filter 208. The input spectrum after being filtered by the first filter 208 is shown in Figure 4B. The input signals are then converted by reduction to IF signals by mixing the signals introduced with signals generated by a LOI. In the second embodiment, the two downlink bands are converted to adjacent bands in the final IF using two fixed LO1 frequencies and two fixed L02 frequencies. The input signals of each service are converted by reduction using different LO frequencies. In this example, the downlink band DSC is converted by reduction with frequencies L01A and L02A, and the downlink band FDD of WCDMA is converted by reduction with the frequencies L01B and L02B. The band-limited input signal of each service is converted by reduction to a first IF bandwidth by a mixer 210 with frequencies L01A and L01B, respectively, and are filtered again by a second filter 212 to eliminate the image frequencies and blockers and amplified by a VGA 214. The first IF spectrum, as transmitted by the VGA 214 is shown in Figure 4C. A second conversion is carried out by reduction by a mixer 216 with L02A and L02B respectively. The second IF spectrum, as transmitted by a filter 218, is shown in Figure 4D. The frequencies L01A, L01B, L02A and L02B are set so that the second conversion by reduction causes the multiple service downlink bands to be located adjacent to each other in the second IF bandwidth as shown in Figure 4D. In this example, the downlink band DSC and the downlink band FDD of WCDMA are converted to adjacent bands and the final IF band. Multiple LO frequencies can also be used to place the multiple service downlink bands anywhere within a second defined IF bandwidth. The final intermediate frequency is sampled by further reduction by an ADC 224 after being processed by the filters 218, 222 and the VGA 220. By minimizing the second IF bandwidth, the sampling frequency of the ADC 224 may be adaptive, so that the power consumption of the final digital downstream to baseband conversion is minimized. Figure 5 is a block diagram of a receiver 300 according to a third embodiment of the present invention. Figures 6A-6D are signal spectrum diagrams in each stage in receiver 300 of Figure 5. A diplexer 302 and a circulator 304 mimic the band of the input spectrum, which is shown in Figure 6A. The band-limited input spectrum is amplified by an LNA 306 and filtered by a first filter 308. The input spectrum after being filtered by the first filtrate 308 is shown in FIG. 6B. The band-limited input signal of each service is converted by reduction to a first IF bandwidth by a mixer 310 with frequency L01A and L01B, respectively and filtered again by a second filter 312 to eliminate image frequencies and blockers; and it is amplified by a VGA 314. The first IF spectrum, as transmitted by the VGA 314, is shown in Figure 6C. In the third embodiment, any of the arbitrary channels of the downlink bands can be converted by reduction to arbitrarily separated channels in the IF band by using a configurable L02. A second conversion by reduction of the two input signals is carried out by a mixer 316 with L02A and L02B, respectively. The second IF spectrum, after being filtered by a filter 318, is shown in Figure 6D. The frequencies L02A and L02B are adjustable such that the second conversion by reduction causes the multi-service downlink bands to be located in the second bandwidth IF separated from each other, as shown in Figure 6D. As an alternative, L01A and L02A can be adjustable and L02A and L02B can be fixed, or both LO can be adjustable. Multiple LO frequencies can also be used to place the multiple service downlink bands anywhere within a second defined IF bandwidth. The final intermediate frequency is further down sampled by an ADC 324 after being processed by filters 318, 322 and VGA 320. By minimizing the second IF bandwidth, the sampling frequency of ADC 324 may be adaptive and This way the energy consumption of the final digital down-to-base band conversion is minimized. Figure 7 is a block diagram of a lookup table (LUT) 400 in the modem of a receiver used to implement adaptive frequency reduction conversions according to the present invention. The desired services, the sampled bandwidth and the second wanted IF are used as inputs for the LUT 400, and the LUT 400 transmits the LO1 and L02 frequency settings and the ADC sampling frequency. The LUT 400 optimizes the frequency plan, the sample frequency and the sampling bandwidth, according to the available services and the SINAD measurements. The LUT can be used in any of the embodiments of the present invention. Figure 8 is a block diagram of a LO frequency synthesizer 500 that synthesizes frequencies for local oscillators, according to the present invention. Since the receivers shown in the second and third modes require multiple LO frequencies, the synthesizer 500 must be able to generate these frequencies. The LO frequency synthesizer 500 comprises a reference oscillator 502 and one or more synthesizers 504. The LO frequency synthesizer optionally may additionally comprise one or more insulators 506 and one or more circulators 508. The reference oscillator 502 generates the frequency reference which is input to the plurality of synthesizers 504. Each synthesizer 504 is tuned to generate IF frequencies according to the frequency settings LO1 and L02 generated by the LUT 400. The IF frequencies generated by the synthesizers 504 are sent to a LO port of a mixer to perform a downconversion of the input signals. A circulator 508 is preferably used to combine the LO frequencies of the two synthesizers in a low loss combination scheme that will minimize the power consumption of the synthesizer. The isolators 506 are provided at the output of each synthesizer 504 to provide sufficient reverse isolation to eliminate frequency pull on any of the synthesizers due to the other synthesizer. Alternatively, buffer buffers may be used in the synthesizers 504 to provide isolation. This allows the synthesizer approach to be further simplified by eliminating insulators 506. Figure 9 is a flow chart of a process 600 for simultaneously processing services Multiple wireless communication in a receiver according to the present invention. More than one service is received simultaneously via wireless interconnection (step 502). Each service is transmitted via a different carrier frequency band. The received carrier frequency bands are converted by reduction to IF bands using a local oscillator (LO) so that the frequency bands converted by reduction are within a single IF band (step 504). In an alternative modality, the SDR simultaneously receives two or more services or channels by using two or more local oscillators summed to independently control the final IF frequencies of two or more services or channels and to adaptively select two or more local oscillating frequencies and the sampling frequency . The SDR according to this embodiment of the present invention, adaptively minimizes the sampling frequency and therefore reduces the power consumption of the ADC and the processing blocks in the modem and increases the overall battery life. This embodiment of the present invention can be implemented both in the base station and in a WTRU. Figure 10 is a block diagram of a receiver 600 for adaptively selecting LO frequencies and a sampling frequency for analog-to-digital conversion of a plurality of input signals received simultaneously, according to the present invention. The receiver 600 comprises an antenna 602, a low noise amplifier 604 (LNA), a mixer 606, two LO 608a and 608b, an adder 618, an ADC 610, a digital IF processing unit 612, a processing unit 614 baseband and a controller 616. Two or more input signals are simultaneously detected by the antenna 602 for two or more services or channels. Each service or channel is transmitted via a different carrier frequency band and is subjected to a unique requirement of signal to interference, noise and distortion (SINAD). The LNA 604 amplifies the received input signals. Each LO 608a, 608b generates a LO signal of a corresponding frequency for each service or channel. Figure 1 illustrates only two LOs as an example, but more than two LOs can be used to place the service downlink or multiple channel bands anywhere within the final IF bandwidth. The frequencies of the LO signals are controlled by the controller 616. The LO signals are summed together by the adder 618 and sent to the mixer 606. The mixer 606 mixes the input signals with the LO signals to convert each RF input signal to an IF signal. In FIG. 1, only one mixing step is illustrated. However, it should be noted that more than one mixing step can be implemented to convert each RF signal to an IF signal. The final IF bands are selected such that the IF bands of the services or channels are spectrally adjacent or overlap each other to some degree. Spectral superposition can result in interference within the receiver to one or both of the bands or channels. Figures 11A-11F are block diagrams of the IF spectra illustrating the frequency shift of the RF input signals to the final IF bands, according to the present invention. The region shaded in Figures 11A-11F represents the frequency channel of interest. The LO frequencies are adjusted so that the reduction conversion causes the input signals to become the final IF bands adjacent or overlapping each other to some degree, as shown in Figures 11A-11F. In Figure HA, the IF bands for the services are adjacent and do not overlap each other.
Therefore, there is no interference caused by one band with the other. In FIG. 11B, the two IF bands overlap each other only in the non-interested frequency channels. In Figures 11C and 11D, a desired channel obtains an interferor, and in Figures HE and 11F, both desired channels obtain interferors. In FIG. 11F, the entire IF band of one service or channel is superimposed on the other IF band. In order to avoid distortion of some region of the IF bands, the sampling frequency can be set at a value at least two times higher than the highest frequency component of the highest IF band. The sampling frequency may be less than said value, insofar as the distortion of a region of an IF band that is not within a channel of interest is acceptable. Therefore, the sampling frequency is determined by the service or channel having the highest frequency component among a plurality of services or channels processed simultaneously. Half of the minimum sampling frequency to avoid interference in a channel of interest is indicated by the continuous arrow in Figures 11A-11F. Half of the minimum required sampling frequency to avoid interference in the frequency band of interest is indicated by a dashed arrow in Figures 11A-11F. The sampling frequency may even be less than that shown by the dashed arrow if the degradation of SINAD, due to the distortion of the higher frequency components within the channel of interest, is tolerable. As the degree of superposition increases from Figure HA to Figure 11F, the sampling frequency decreases, but the interference in the channels of interest increases. Therefore, the overlap condition and the sampling frequency can be selected considering both the sampling frequency and the interference. The selected IF bandwidth and the superposition condition in the final IF band are adaptively adjusted as a function of the measured SINAD of the simultaneous services or channels of interest. Each service or channel has a minimum SINAD criteria that must be satisfied. Referring again to Figure 10, the baseband processing unit 614 measures the SINAD under various overlap conditions and the controller 616 selects the overlap condition with the lowest sampling frequency that satisfies the minimum SINAD criteria such as the frequency of optimal sampling. The ADC 610 converts the IF band signals to digital signals at the set sampling frequency - - by the controller 616. The digital IF processing unit 612 and the baseband processing unit 614 process the digital signals for the services. The digital IF processing unit 612 performs the final frequency conversion from IF to baseband. The digital IF processing unit 612 separates the services from each other. By adaptively controlling the final IF bands of the services or channels, the sampling frequency can be minimized in an adaptive manner. Minimizing the sampling frequency reduces the power consumption of the ADC and the processing blocks in the modem and increases the total battery life. The channel conditions (such as the distance of the cells, changes in adjacent channels, etc.) change with time. The selection of the superposition condition and the optimal sampling frequency is reevaluated at a certain speed. Because the presence or absence of adjacent channels is unknown for the WTRU, it can change at a faster rate than anticipated for the reassessment described above, in order to avoid an unacceptable sudden degradation of connections, the evaluation of overlap spectrum and the selection of the optimal sampling frequency can be confined to unconnected or free periods, or periods in which only packet data is received. During periods in which sudden degradation is not acceptable, the receiver operates without the spectral superposition at the highest sampled frequency that supports this condition. Regardless of the selection of the superposition condition and the optimum sampling frequency, the sampling frequency can be further reduced by deliberately introducing distortion in the frequency band, which is not of interest. Figure 12 is a flowchart of a process 800 for adaptively selecting the sampling frequency for analog-to-digital conversion of a plurality of input signals in a receiver, in accordance with the present invention. A receiver receives two or more input signals for two or more services or channels simultaneously (step 802). Each service or channel is subject to a minimum SINAD requirement. The input signals are converted to IF band signals by mixing the input signals with LO signals (step 804). The LO frequencies are adjusted such that the IF band signals converted from the input signals are spectrally adjacent or overlap with each other to some degree. The SINAD of the services or channels is measured in each of the plurality of spectral superposition conditions (step 806). The LO frequencies and the sampling frequency for analog-to-digital conversion of the IF signals is selected based on the SINAD measurement results (step 808). Steps 806 and 808 are preferably repeated, periodically or non-periodically. Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used only without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the invention. present invention.