Presently, base station receivers for AMPS and D- AMPS are usually designed as double superheterodyne receivers which perform an analog downconversion of each individual narrowband (approximately 30 kHz) channel to a fixed (common for all channels) intermediate frequency. In other words, the same fixed intermediate frequency is used irrespective of which channel the receiver is tuned to. Analog-to-digital conversion of each narrowband channel is then performed and subsequent signal processing is done digitally.

An example of a conventional double superheterodyne receiver system for n channels is illustrated in Figure 1. In Figure 1, desired bands are received by a first bandpass filter 10 which is connected to first pairs of first local oscillators 20ι_, 2O ₂ , ...20 _n and first mixers 30ι, 30 ₂ , ...30 _n so that each received channel is converted to a common fixed intermediate frequency. A plurality of second bandpass filters 40]_, 40 ₂ , ...40 _n are connected to the first mixers 30^, 30 ₂ , ...30 _n , respectively for passing through narrowband channels of approximately 30 kHz. The outputs of the second bandpass filters 40ι, 40 ₂ , ...40 _n are connected to second pairs of second local oscillators 50ι_, 50 ₂ , ...50 _n and

second mixers 60^, 6O ₂ , ...60 _n for performing an analog down conversion of each individual narrowband channel from the second bandpass filters 40χ, 40 ₂ , ...40 _n . The outputs of the second mixers 60^, 6O ₂ , ...60 _n are connected to a plurality of third bandpass filters 10χ , IO2 , ...70 _n . Analog-to-digital converters 80τ_, 8O ₂ , ...80 _n perform analog-to-digital conversion of each narrowband channel and then signal processing is performed digitally by a plurality of digital signal processors 90ι, 90 ₂ , • • .90 _n .

It is also known to use a wideband receiver in which the whole frequency spectra allocated to the operator is downconverted to a suitable intermediate frequency interval and then converted from analog to digital. The selection of each narrowband channel and further processing is then done digitally. Figure 2 illustrates an example of this conventional wideband receiver where a signal is input to a first bandpass filter 15 and then downconverted to the intermediate frequency interval by a local oscillator 25 and a mixer 35. The output of the mixer 35 is input to a second bandpass filter 45 and then converted to a digital signal by the analog-to-digital converter 85. The output of the analog-to-digital converter 85 is input to a plurality of digital signal processors 95χ, 952, ••• ⁹⁵ n for further processing.

In the application of wideband receivers to the AMPS frequency plan, certain difficulties exist which prevent sufficient resolution from being achieved for the required dynamic range of the wideband receiver. To better illustrate these problems, an overview of the AMPS frequency is provided below in Table 1.

TABLE 1

A" 824-825 MHZ (1 MHZ bandwidth)

A 825-835 MHZ (10 MHz)

B 835-845 MHz (10 MHz)

A' 845-846.5 MHz (1.5 MHz)

B' 846.5-849 MHz (2.5 MHz)

As seen in Table 1, the full A- or B-band utilizes 12.5 MHz bandwidth each. Because of the distribution of the bands, a wideband receiver needs to cover 22.5 MHz bandwidth (824-846.5 MHz) for the full A-band and 14 MHz bandwidth for full B-band coverage (835-849 MHz) , respectively. Because only the A- and B-bands were originally allocated for mobile telephone use, the later addition of the extended bands A''-, A'- and B'-bands caused the differences in the bandwidth which are necessary for fully covering the A- and B-bands.

To achieve full B-band coverage in a wideband receiver, a sampling frequency of at least 28 MHz (2 x 14 MHz, which is the bandwidth for full B-band coverage) is needed. The 28 MHz sampling frequency is within the limits of the present technology for sufficient resolution to achieve the required dynamic range for the wideband receiver. However, to achieve full A-band coverage, a sampling frequency of more than 45 MHz (2 x 22.5 MHz, the bandwidth for full A-band coverage) is required. This sampling frequency is beyond the present technology for an analog-to-digital converter with sufficient resolution.

In order to overcome this problem of insufficient

resolution, a wideband receiver as illustrated in Figure 3, for example, has been proposed. In the wideband receiver of Figure 3, a first bandpass filter 100 receives the A' ' ^' -, A'- and A-bands and is connected to a pair of first local oscillator 110 and a firεt mixer 120 which frequency transpose the A-, A'-, and A' '-bands to an intermediate frequency band. The output of the first mixer 120 is connected to second and third bandpass filters 130 and 131 for passing the A- and A' '-bands and the A'-band therethrough, respectively. The outputs of the second and third bandpass filters 130 and 131 are connected to pairs of second and third local oscillators 140 and 141 and second and third mixers 150 and 151. The outputs of the second and third mixers 150 and 151 are input to fourth and fifth bandpass filters 160 and 161, respectively. The frequency of the second local oscillator 140 and the frequency of the third local oscillator 141 are chosen so that the A''- and A-bands, and the A'-band, respectively, are transposed to a nearly continuous frequency band having a total bandwidth of less than approximately 15 MHz. As a result, the required sampling frequency becomes 30 MHz (2 x the total bandwidth of approximately 15 MHz) . The nearly continuous frequency band is input to an analog- to-digital converter 170. The output of the analog-to- digital converter 170 is input to a plurality of digital signal processors 180^, I8O2, ...180 _n . The frequencies of the second and third local oscillators 140 and 141 must be chosen so that a sufficient guardband is provided which prevents the requirements on the anti-aliasing filters from being too stringent.

Figure 4 illustrates another proposed solution which provides a sufficient resolution for the required dynamic range of the wideband receiver. In Figure 4, a first bandpass filter 105 receives the A-, A'-, and A''-

bands and passes these bands through to a pair of a local oscillator 115 and a first mixer 125. The transposed A- and A' '-bands are input to a second bandpass filter 135 and the transposed A'-band is input to a third bandpass filter 136. The outputs of the second and third bandpass filters 135 and 136 are input to second and third mixers 155 and 156 which are connected to a common local oscillator 145 so that Fj_ _n - Fχ. ₀ from one mixer and FL _O - Finfrom the other mixer are used. The outputs of the second and third mixers 155 and 156 are input to fourth and fifth bandpass filters 165 and 166 to provide a nearly continuous frequency band to an analog-to-digital converter 175. The output of the analog-to-digital converter 175 is input to a plurality of digital signal processors 185ι, 185 ₂ ,

...185 _n . In this wideband receiver, one of the bands iε inverted, while the other band is non-inverted, but the inverted band iε corrected by the digital signal processors 185ι, 185 ₂ , ...185 _n . In both of the wideband receivers proposed in

Figures 3 and 4, a double superhet receiver is used with three mixers and at least two local oscillators. The embodiments of the present invention are directed to a wideband single superheterodyne receiver which fully covers a desired band with only one mixer and one local oscillator.

SUMMARY An object of the present invention is to provide a wideband receiver which fully covers a desired bandwidth of frequencies. More particularly, the present invention is directed to a wideband εuperheterodyne receiver for providing full coverage of the deεired band with only one mixer and one local oscillator.

Another object of the preεent invention is to utilize an analog-to-digital converter which converts two separate parts of a spectrum, where said spectrum has a total bandwidth greater than the Nyquist frequency of the analog-to-digital converter, and to take advantage of the aliasing characteristics during the sampling proceεε in a positive manner εo that the wideband receiver provides full coverage of the desired band. A still further object of the preεent invention is to provide full A-band coverage of the AMPS frequency plan by a wideband receiver having only one mixer and one local oscillator.

These objects of the present invention are fulfilled by providing a wideband receiver for full coverage of a desired band comprising a local oεcillator operating at a tranεpoεing frequency, a mixer connected to εaid local oscillator for receiving predetermined frequency bands and transposing said predetermined frequency bands to transposed frequency bands in responεe to εaid tranεpoεing frequency, and an analog- to-digital converter operating at a εa pling frequency for aliasing down said transposed frequency bands to achieve full coverage of the desired band. By using the aliaεing characteristics of the analog-to-digital converter in a positive manner, the wideband receiver provideε full A-band coverage with only one mixer and one local oscillator. Thereby the analog parts of the wideband receiver are minimized so that the wideband receiver is εmaller in size, consumeε leεε power and haε a high manufacturing yield.

The objects of the present invention are also fulfilled by a method for providing full coverage of a desired band with a wideband receiver comprising the stepε of operating a local oεcillator at a transposing

frequency, receiving predetermined frequency bandε with a mixer and transposing said predetermined frequency bands to transposed frequency bands in response to said tranεpoεing frequency, and aliasing down said transposed frequency bands by an analog-to-digital converter operating at a sampling frequency to achieve full coverage of the desired band. This method similarly utilizes the inherent aliasing characteriεtics of this sampling procesε taking place in the analog-to-digital converter εo that full coverage of a deεired band is provided with only one mixer and one local oscillator.

Further scope of applicability of the present invention will become apparent from the detail deεcription given hereinafter. However, it εhould be understood that the detailed description and specific examples, all indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to thoεe εkilled in the art from thiε detailed deεcription.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illuεtration only, and thuε are not limitative of the preεent invention, wherein:

Figure 1 illustrates a conventional receiver εystem for n narrowband channels where each channel is proceεsed in a double superheterodyne receiver which converts each narrowband channel;

Figure 2 illustrates a conventional wideband receiver which converts the whole frequency spectra and performs digital processing for n narrowband channels; Figure 3 illustrates a proposed wideband receiver having three mixers and three local oscillators, making

it possible to convert two separate parts of a spectrum into a nearly continuous frequency band with a bandwidth less than the original spectrum bandwidth;

Figure 4 illustrates a proposed wideband receiver having three mixers and two local oscillators, making it possible to convert two separate parts of a spectrum into a nearly continuous frequency band with a bandwidth less than the original spectrum bandwidth;

Figure 5 illustrates a wideband receiver for an embodiment of the present invention; and

Figure 6 illuεtrateε an example of a frequency plan for the wideband receiver used in an embodiment of the present invention.

DETAILED DESCRIPTION Figure 5 illustrateε a wideband receiver for an embodiment of the preεent invention. In thiε embodiment, a wideband, εingle εuperheterodyne receiver is provided for full coverage of a deεired band with only one mixer and one local oscillator. In Figure 5, a εpectrum is input to a firεt bandpaεε filter 200 which paεses through desired frequency bands. The desired frequency bands pasεing through the first bandpass filter 200 are input to a mixer 220. The mixer 220 is connected to a local oscillator 210 which operates the mixer 220 at a transpoεing frequency. By operating the mixer 220 at the tranεpoεing frequency, tranεpoεed frequency bandε are outputted from the mixer 220. The output of the mixer 220 iε input to εecond and third bandpaεs filters 230 and 240 for pasεing the transposed frequency bands therethrough. The transposed frequency bands are input to an analog-to-digital converter 250 which converts the transposed frequency bands to digital εignalε.

In the εampling process, the analog-to-digital converter 250 operates at a predetermined εampling

frequency which aliaεes down the transposed frequency bands to inverted and non-inverted frequency bands. The output of the analog-to-digital converter 250 is input to a plurality of digital signal processors 260^, 26O ₂ , ...260 _n for further procesεing of the frequency bandε. The digital signal procesεorε 260;j_, 26O ₂ , ...260 _n can eaεily proceεε the inverted frequency band aliaεed down by the analog-to-digital converter 250. For simplicity, only the parts that are essential for the understanding of the function are shown in the figures and mentioned in the description (the filters, mixers, local oscillators, analog-to-digital converters) . However, in the actual implementation of the wideband receiver, various additional circuitry as would be obvious to one of ordinary skill in the art is neceεsary to ensure that sufficient signal-to-noise ratios are achieved, such as different amplifiers for example.

In the present embodiment, aliasing, which is uεually thought of aε an undesired property, is used in a positive manner to make it posεible to deεign a wideband receiver for fully covering a deεired band in a εpectrum with only one mixer and one local oscillator. The analog input spectra consiεtε of two deεired partε with bandwidthε Bi and B ₂ respectively, separated by a non-desired band with bandwidth G _a , where Bi + G _a + B ₂ > f _N yq,and where f yqiε the Nyquist frequency of the analog-to-digital converter 250. The aliasing is used to digitally transpoεe the part with the bandwidth B2 εo that the digital (after analog-to-digital converεion) spectra consistε of two deεired parts with bandwidths Bi and B2 respectively, now εeparated by a non-desired band with bandwidth G^, where Bi + G^ + B ₂ < fNyq- ^B Y advantageously utilizing the aliasing characteristicε of the analog-to-digital converter 250, a sampling frequency can be used that is within the known

limitations for present analog-to-digital converters (approximately 39 MHz) . Thereby, even when the sampling frequency iε less than twice the bandwidth of the spectrum, the Nyquist criteria is fulfilled by advantageously utilizing the aliasing characteristics.

When the desired band coverage is for the A-band of the AMPS frequency plan, for example, the wideband single superheterodyne receiver operateε aε will be deεcribed aε followε with reference to Figure 6. Thiε example iε used to only illustrate the operation of the wideband receiver for the present embodiment and other considerations muεt be taken into account when actually deεigning the wideband receiver, such as sample frequency versus data rate, anti-aliaεing filter εtructureε, etc. , which are neglected in thiε example. The full A-band iε input to the firεt bandpaεε filter 200 for paεεing through the A"-, A-, and A'-bands which include the frequencies of 824-835 and 845-846.5 MHz. These frequency bands are then input to the mixer 220 which is operated by the local oscillator 210 at the tranεpoεing frequency of 803 MHz and tranεpoεeε the A''- and A-bands to between the frequencieε of fi and f2 (corresponding to 21 and 32 MHz) and the A'-band to between the frequencieε of f3 and f4 (which correεponds to 42 and 43.5 MHz) as illustrated in Figure 6. The second bandpasε filter 230 paεses through the A- and A' '-bandε between 21 and 32 MHz and the third bandpaεs filter 240 paεεes through A'-band frequencieε between 42 and 43.5 MHz. With a sampling frequency of f _s = 39 MHz for the analog-to-digital converter 250, the A'-band is aliased down to between 3 and 4.5 MHz (non-inverted) and the A''- and A-bands are aliased down to between 7 and 18 MHz, inverted. Although it iε theoretically poεεible to use a εampling frequency of approximately 33.5 MHz in

this example, the sampling frequency should be higher, near the 39 MHz used in this example, for practical purposeε to provide a sufficient guardband. The theoretical minimum sampling frequency can be calculated as follows. By placing f _s between f2 and f3 so that f3 - f _s = f _s - f2 - (f4 - f3) [Equation 1] the "A'-band of the εpectrum is made to alias around f _s without overlapping the A''- and A-bands. The A''- and A-bands alias around f1 such that fi = f^2 [Equation 2]. Thereby, Equation 1 can be rewritten as 2f _s = f2 + f4 = f2 - f1 + f4 - f1 + 2fχ [Equation 3]. Because 2f1 = f _s according to Equation 2, the relation f _s = f2 - f1 + f4 - f1 = 11 MHz + 22.5 MHz = 33.5 MHz for this example. The aliased down A-band iε included within the frequencieε from 3 to 18 MHz with a guardband between 4.5 and 7 MHz. The A- and A' '-bandε are inverted while the A'-band iε non-inverted, but the A- and A' '-bandε are eaεily proceεsed by the digital signal processors 260ι, 26O2, ...260 _n which receive the output from the analog-to-digital converter 250. By utilizing the inherent aliasing characteriεtics of the sampling process which takes place in the analog- to-digital converter 250, a wideband superheterodyne receiver is provided for full A-band coverage with only one mixer and one local oscillator. More generally, by advantageously uεing the aliaεing characteristicε, a wideband receiver may be deεigned for fully covering a deεired band with only one mixer and one local oεcillator. Aε a reεult, the analog partε of the wideband receiver are minimized εo that the wideband receiver iε εmaller, conεumes less power, has a higher manufacturing yield and haε a reduced manufacturing coεt.

The invention being thus deεcribed, it would be obviouε that the εame may be varied in many ways. Such variations are not to be regarded aε a departure from

the spirit and εcope of the invention, and all εuch modification as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.