HK1036714A - Dual-mide receiver for receiving satellite and terrestrial signals in a digital broadcast system - Google Patents

Description

Dual mode receiver for receiving satellite and terrestrial signals in digital broadcasting system

The invention relates to a receiver for a digital broadcasting system, such as the proposed Digital Audio Radio Service (DARS), having a combined structure for receiving satellite signals and terrestrial signals.

The broadcast system employs one or more terrestrial repeaters to overcome line of sight (LOS) satellite signal reception obstacles for both fixed and mobile radio receivers. The terrestrial repeater receives QPSK modulated, time-division multiplexed (TDM) satellite signals, performs baseband processing of the satellite signals, and retransmits the satellite signals via multi-carrier modulation (MCM). A digital filter is employed that satisfies the requirements of QPSK satellite signal reception to reduce receiver complexity and acts as a down-sampling filter prior to MCM demodulation of the terrestrial signal.

Fig. 1 shows a digital broadcasting system for transmitting satellite signals and terrestrial signals;

fig. 2 is a block diagram illustrating a broadcast segment and a terrestrial repeater segment of a digital broadcasting system according to a preferred embodiment of the present invention;

fig. 3 illustrates a frequency scheme for satellite and terrestrial signals in a full diversity broadcast system, according to a preferred embodiment of the present invention;

FIG. 4 is a block diagram of a satellite signal and terrestrial signal receiver constructed in accordance with a preferred embodiment of the invention;

FIG. 5 is a block diagram of a receiver branch for Quadrature Phase Shift Keyed (QPSK) satellite signals constructed in accordance with a preferred embodiment of the present invention;

FIG. 6 illustrates the frequency response of a Surface Acoustic Wave (SAW) filter for satellite and terrestrial signals in accordance with a preferred embodiment of the present invention;

FIG. 7 illustrates the frequency response of a digital filter for satellite signals in accordance with a preferred embodiment of the present invention;

fig. 8 is a block diagram of a receiver branch for a multi-carrier modulated (MCM) terrestrial signal constructed in accordance with a preferred embodiment of the invention;

FIG. 9 illustrates the frequency response of the MCM ground signal after surface acoustic wave filtering, according to a preferred embodiment of the invention;

FIG. 10 illustrates the frequency response of the MCM ground signal after digital filtering, according to a preferred embodiment of the invention;

FIG. 11 is a block diagram of a receiver configured to receive QPSK satellite signals and MCM terrestrial signals; and

fig. 12 is a block diagram of a receiver having a combined structure for receiving and demodulating QPSK satellite signals and MCM terrestrial signals according to the preferred embodiment of the present invention.

Fig. 1 shows a digital broadcast system 10 including at least one geostationary satellite 12 for line of sight (LOS) satellite signal reception generally indicated at 14 by a radio receiver. Another geostationary satellite 16 may be provided at a different orbital location, as discussed below in connection with fig. 3, for time and/or space diversity purposes. The system 10 further includes at least one terrestrial repeater 18 for retransmitting satellite signals in a geographical area 20 that is obscured by tall buildings, hills and other obstructions to LOS reception. The radio receiver 14 is preferably configured for dual mode operation to receive satellite signals and terrestrial signals and select one of the signals as the receiver output.

Referring now to fig. 2, the broadcast segment 22 and the terrestrial repeater segment 24 of the system 10 are illustrated. The broadcast segment preferably includes a broadcast channel encoded into a 3.68 megabit/second (Mbps) Time Division Multiplexed (TDM) bit stream, as shown at block 26. The TDM bit stream contains 96 main rate channels of 16 kilobits per second (kbps) and additional information for synchronization, de-multiplexing, broadcast channel control and services. The broadcast channel coding preferably includes MPEG audio coding, Forward Error Correction (FEC) and multiplexing. The resulting TDM bit stream is modulated using Quadrature Phase Shift Keying (QPSK) modulation prior to transmission over the satellite uplink 30, as shown at block 28.

With continued reference to fig. 2, the terrestrial repeater segment includes a satellite downlink 32 and a demodulator 34 for QPSK demodulation to obtain baseband TDM bit streams. A puncturing and delay block 36 removes the select bits that can be re-inserted at the radio receiver to reduce the TDM bit rate from 3.68 Mbps to 3.067 Mbps and also delays the time diversity delay (if any) between the transmission of the entire TDM bit stream from satellites 12 and 16. The delayed, reduced rate bit stream undergoes multi-carrier modulation at block 38 before being amplified by amplifier 39 and transmitted from a terrestrial repeater tower 40. The multi-carrier modulation preferably comprises dividing the 3.067 mbps tdm bit stream in the time domain into 432 parallel paths, each transmitting 7100 bits/sec. These bits are paired as two-bit symbols, identified as a complex imaginary (I) component and real (Q) component, respectively. Thus, the complex symbol rate is 3550 symbols/sec. A432 parallel complex number is provided as the frequency coefficient input to a discrete inverse Fourier transform converter, preferably using a 512 coefficient Inverse Fast Fourier Transform (IFFT), with 2ⁿInput and output operations are performed with n =9 and 80 input coefficients set to zero. The output of the IFFT is a set of 432 QPSK quadrature sine coefficients, which constitute 432 narrowband quadrature carriers, support a symbol rate of 3550 per second, and have a symbol period of 280 microseconds.

A frequency plan view of a full diversity, two-satellite broadcast system 10 is shown in fig. 3. In a preferred embodiment of system 10, satellites 12 and 16 of FIG. 1 each broadcast the same programs A and B. The "early" satellite 12 transmits programs a and B prior to its transmission via the "late" satellite 16. The frequency scheme allocates frequency bands to each of the four QPSK modulated satellite signals as shown at 42, 44, 46 and 48, respectively, in fig. 3. In addition, two frequency bands 50 and 52 are allocated to multicarrier modulated program a and B signals transmitted from terrestrial repeaters that retransmit the signals from the early satellites 12 with a delay sufficient to time synchronize with the signals transmitted by the late satellites 16. In the frequency scheme, the channel spacing is relatively small, with each of the six bands 42-52 occupying approximately 2.07 megahertz (MHz), for a total bandwidth of 12.5 MHz.

Referring to fig. 4, there is illustrated a dual mode radio receiver comprising a first branch 54 for receiving a QPSK signal from the early satellite 12, a second branch 56 for receiving a QPSK signal from the late satellite 16 and an MCM signal from a terrestrial repeater 18, and a combining unit 58 for generating a receiver output from the two received signals. The two branches 54 and 56 allow full diversity reception. The QPSK/MCM branch 56 of the radio receiver is implemented as a dual-mode receiver branch for satellite and terrestrial signal reception. The QPSK signals received from satellites 12 and 16 are demodulated at blocks 60 and 62, respectively. An MCM signal from the terrestrial repeater 18 (containing the delayed, multicarrier modulated signal transmitted by the early satellite 12) is also demodulated as shown at block 64. A depuncture unit 66 reinserts the bits into the demodulated signal from the terrestrial repeater to increase the bit rate to that of the original TDM bit stream.

The QPSK/MCM receiver branch 56 is configured to detect when a terrestrial repeater signal is present and select the terrestrial repeater signal via a selection unit 68 in place of the signal from the late satellite 16, as indicated at block 67. In a broadcast system having at least one satellite and at least one terrestrial repeater, terrestrial signals in bands 50 and 52 of fig. 3 may be absent or negligible when a radio receiver is in a rural area outside the range of the terrestrial repeater. If the radio receiver is mobile and the user is in use close to a city or downtown area, both satellite and terrestrial signals can be received. If the radio receiver is mobile and used while driving in a city, in many cases only ground signals can be received, since there is no LOS signal reception possible from the satellite. If the strength of the terrestrial signal exceeds a predetermined limit, the dual mode receiver branch 56 of the radio receiver switches from receiving the signal from the satellite 16 to receiving the signal from the terrestrial repeater 18. The IQPSK demodulators 60 and 62, MCM demodulator 64, depuncture unit 66, ground detection unit 67 and selection unit 68 shown in fig. 4 are described in more detail below.

The signal at the output of QPSK demodulator 60 in receiver branch 54 and the signal at the output of selection unit 68 in receiver branch 56 are TDM demultiplexed and decoded to recover the baseband bit stream, as shown in blocks 70 and 72 of fig. 4. As shown at block 74, the recovered bit stream from the satellite 12 is delayed at the receiver branch 54 by an amount corresponding to the delay broadcast from the early 12 and late 16 satellites to time synchronize the bit stream with the bit stream generated by the receiver branch 56. The signals from the receiver branches 54 and 56 are then subjected to post-detection diversity combining as shown at block 58 before MPEG audio decoding at block 78. It will be appreciated that the radio receiver need not support satellite diversity and can therefore be implemented by only the QPSK/MCM branch 56, without the QPSK branch 54. In such a radio receiver, the post-detection combining unit 58 may also be omitted.

As shown in fig. 3, the level of the terrestrial signal is substantially higher than the satellite signal and may be, for example, on the order of about 30 decibels (dB) higher than the satellite signal. As previously mentioned, the channel spacing is relatively small in the frequency plan. Therefore, if a terrestrial signal is present in an adjacent channel as shown in fig. 3, filtering by high-stopband attenuation is required to decode the satellite signal. Typically, the frequency separation between the satellite and terrestrial signal channels is increased to avoid such filtering. When the spacing is sufficient, a channel filter is used to reject adjacent channels.

According to one embodiment of the invention, channel selection is performed using a filter that does not completely suppress adjacent channels. As will be discussed below, the location of terrestrial repeater frequency bands 50 and 52 in the lower portion of the frequency plan (and near frequency bands 46 and 48 of the late satellites 16, respectively) facilitates selection of either the satellite signal or the terrestrial signal for output by the receiver. Filtering will be described in connection with QPSK demodulation and then MCM demodulation before describing filtering in a combined QPSK/MCM dual mode receiver branch (fig. 12) constructed in accordance with a preferred embodiment of the present invention.

A schematic block diagram of a QPSK satellite signal receiver branch 80 is shown in fig. 5. An antenna 82 and Low Noise Amplifier (LNA)84 at the radio receiver receive a signal at a carrier frequency of approximately 2.3 gigahertz (GHz). The signal is down-converted to a first Intermediate Frequency (IF) of about 135MHz by a mixer 86 and a local oscillator 88. The signal from mixer 86 is provided to a low loss Surface Acoustic Wave (SAW) Intermediate Frequency (IF) filter 90 and to a second mixer 92 and local oscillator 94 down-converted to a second IF of about 3.68 MHz.

A weak or "leaky" SAW filter is preferred over a strong SAW filter with better adjacent channel rejection. As shown in fig. 6, a terrestrial channel 50, located directly adjacent to the satellite channel 46, is partially within the SAW filter passband, and the attenuation of this interfering signal channel 50 is only about 6 dB. Although a strong SAW filter is better able to remove an adjacent channel (e.g., channel 50), a strong SAW filter may introduce phase distortion and be more expensive to implement than a weak SAW filter.

The QPSK satellite signal branch 80 of fig. 5 includes a sampler 96 that samples the received signal at the output of the SAW filter 90 at four times the sampling rate of the second IF. An analog-to-digital (A/D) converter 100 performs A/D conversion of the sampled signal, and a digital filter 102 removes adjacent channels (e.g., channel 50) from the digitized satellite signal. The digital filter 102 is preferably matched to a transmitter filter at the broadcast station. Depending on the SAW filter 90, and the signal-to-noise ratio (SNR) after the SAW filter 90, the digital filter 102 may have a stop band attenuation of 30dB or more. The output of the digital filter 102 is then processed through a sample switch and latch device 104 to recover the TDM signal from the QPSK modulation performed by the broadcast station.

The digital filter 102 is preferably a root-raised-cosine (RRC) filter conventionally used for QPSK modulation and demodulation. In the preferred embodiment, the RRC filter has a sampling rate of 4 times IF, or 8 times the rate of symbols transmitted from the satellite signal of the originating broadcast station. Also, a roll-off factor (roll-off) of α = 0.15 is selected. As shown in fig. 7, the frequency response of the RRC filter has a passband ripple of 0.1 dB and a stopband ripple of 40 dB. Fig. 7 provides three curves representing the ideal RRC frequency response, the results of the Remez algorithm, and the RRC frequency response after coefficient quantization. A 136-tap, linear-phase, Finite Impulse Response (FIR) filter with 10-bit fixed point coefficients and a word length of 16 bits can meet this RRC filter specification.

An MCM demodulator is shown in fig. 8 for MCM demodulation, an FFT used to implement the filter bank at the radio receiver, and corresponding to the IFFT described above in connection with MCM modulation at terrestrial repeaters. The input to the FFT is sampled according to several parameter choices for MCM transmission, as shown in fig. 8. The sampling frequency depends on the MCM symbol frequency Fs, which corresponds to the number of MCM symbols transmitted per second from the terrestrial repeater. In addition, the sampling frequency depends on the length of the FFT and the length of the guard interval associated with each MCM symbol. The sampling frequency is preferably F₄=Fs^*FFTLEN^*(1+ GUARDLEN _ REL), where FFTLEN corresponds to the length of the FFT (e.g., 512), GUARDLEN _ REL corresponds to the length of the guard interval relative to the effective length or symbol duration (e.g., 280 microseconds), and Fs corresponds to the MCM symbol frequency. The MCM symbol frequency Fs is the bit rate divided by the number of bits per MCM symbol. For example, the MCM signal bit rate may be 3.067 million bits per second (Mbps) and the number of bits per symbol may be 864 or 432.

Please continue to refer to fig. 8, in wirelessThe electrical receiver receives an MCM signal at approximately 2.3 GHz via antenna 106 and Low Noise Amplifier (LNA) 108 and is down-converted to an IF at approximately 135MHz by a mixer 110 and a local oscillator 112 before being processed by SAW filter 114. The signal is band limited by the SAW filter 114 to avoid aliasing components. The sampling frequency in the bandwidth of the SAW filter satisfies the Nyquist criterion (Nyquist criterion) for sampling the signal. The received MCM signal is then down-converted to a second IF of approximately 4.60 MHz using a second mixer 116 and a second local oscillator 118. The signal is sampled by a sampler 120 at a frequency band higher than the signal, i.e. at a sampling frequency F₂＞=2^*F₁And sampling is performed. As shown in fig. 9, the required sampling frequency is high (e.g., 4 times higher than the required signal bandwidth) compared to the required bandwidth of the terrestrial signal. After the a/D conversion in block 122, a digital filter 124 is used to reject the adjacent channel. Since the adjacent satellite channel 46 is at a level significantly lower than the terrestrial signal 50 (i.e., on the order of about 30dB lower), the digital filter 124 may be a low pass filter, rather than a band pass filter. The adjacent satellite channels 46 are shown only as noise after a/D conversion and down sampling. The resulting spectrum after digital low-pass filtering is shown in fig. 10. The bandwidth is now equal to F₃. The signal then undergoes down-sampling so that at a lower sampling frequency F₄≥2^*F₃And (4) showing. Frequency F₂And F₄Is selected such that F₄Is equal to N^*F₂Where N is an integer, such as 4.

As shown in fig. 8, after down-sampling at block 126, the output of the digital low pass filter 124 is provided to the FFT as part of the MCM demodulation process. The samples are converted to a vector by serial-to-parallel conversion and then transformed to the frequency domain by FFT before being decoded by the inverse mapping process. The mapping process converts the output of the complex-valued FFT in the form of a data vector into an output bit stream.

QPSK modulation is an effective method for satellite broadcasting, while MCM modulation is useful for terrestrial broadcasting. For systems such as for suburban and rural areas with satellite broadcasts and urban centers blocked by tall buildings with terrestrial broadcasts, a combined receiver is required to receive both satellite and terrestrial signals. One possible dual mode receiver is shown in fig. 11. This dual mode receiver may be used as the satellite/terrestrial branch 56 in the radio receiver 14 of fig. 1. If the same frequency is used for both the satellite signal and the terrestrial signal, a common tuner 129 may be used. The QPSK branch 130 and the MCM branch 132 of the dual-mode receiver may be identical to the QPSK demodulator and the MCM demodulator, respectively, described above in connection with fig. 5 and 8.

In accordance with a preferred embodiment of the present invention, a dual mode receiver, such as a satellite/terrestrial branch for implementing a radio receiver, uses a combined structure for implementing QPSK and MCM demodulation. This common structure is shown in fig. 12. The dual mode receiver shown in fig. 12 has advantages because it employs only one SAW filter and only one digital filter, and thus reduces cost and complexity compared to the receiver shown in fig. 11.

With continued reference to FIG. 12, an antenna 134 and LNA 136 are provided for receiving satellite and terrestrial signals, preferably in the frequency range of 2.332 to 2.345 GHz. The received satellite and terrestrial signals are provided to the same SAW filter 132, which is preferably a weak or "leaky" SAW filter. As previously mentioned, a weak SAW filter is preferred over a strong SAW filter with better adjacent channel rejection performance, since a strong SAW filter may introduce phase distortion and is also more expensive to implement. As shown in fig. 6, the passband of the weak SAW filter attenuates the terrestrial signal by only about 6dB in adjacent channels. This partial suppression of adjacent channels is advantageous because it allows the detection of terrestrial signals. The dual-mode receiver is configured to select the received terrestrial signal for receiver output over the received satellite signal whenever the terrestrial signal exceeds a predetermined limit. Thus, dual-mode receivers essentially constantly search for terrestrial signals and select satellite signals only when terrestrial signals are not present.

In the illustrated embodiment, a system for use in a computer system is providedA Phase Locked Loop (PLL) 139 of the two voltage controlled local oscillators 140 and 142, along with corresponding mixers 144 and 146, are selectively tuned for down-converting the QPSK and MCM signals to two different second IFs (i.e., 3.68 and 4.60 MHz, respectively) as described above in connection with fig. 5 and 8. For example, oscillators 140 and 142 can each be locked to a 14.72 MHz reference oscillator, and can use a 230kHz phase comparator frequency. At mixer 144, satellite and terrestrial signals having different frequency bands are mixed with different local oscillator input frequencies to down-convert the signals to the same IF at about 135 MHz. For example, the mixer input frequency is F_L01For ground signal F_terr-F_IFAnd for satellite signals as F_terr-2．07 MHz-F_IF。

With respect to mixer 146, the sampling frequency differs depending on whether the receiver uses terrestrial or satellite signals for the receiver output. The mixer 146 is preferably retuned to achieve a second IF that is one-quarter of the sampling frequency used. The sampling frequency used is preferably an integer multiple of 2.3 MHz for MCM terrestrial signals and an integer multiple of 1.84 MHz for QPSK/TDM satellite signals. Thus, retuning mixer 146 facilitates simplification of I/Q generation. Feedback data from the ground detection circuitry described below is provided to superheterodyne PLL circuitry 139 to control the operation of local oscillators 140 and 142 depending on whether a sufficiently strong ground signal has been detected and used for receiver output in place of the satellite signal.

The digital filter 148 of fig. 12 is implemented such that the frequency response of the matched filter (e.g., the RRC filter described above in connection with fig. 5 and 7) needed for QPSK demodulation is also satisfied prior to down-sampling of the MCM signal for FFT processing (e.g., at sampling frequency F)₄=N^*2.3 MHz, where N =8) digital filter requirements. Upon initial power-up of the receiver, the receiver configures local oscillators 140 and 142 for the satellite signal down to a second IF of 3.68 MHz. The sampling and a/D conversion of the satellite signals at blocks 150 and 152 are as previously described. For the RRC filter, a sampling rate ofQuadruple IF (or eight times symbol rate). The passband of the RRC filter is configured such that the filter does not pass energy of adjacent terrestrial signals. If there is a terrestrial signal of sufficient energy in channel 50 near the satellite signal delivered by the SAW filter, a difference in signal energy can be detected between the input and output of the RRC filter. This is accomplished by the ground signal detector 154 in fig. 12. The ground signal detector 154 compares the signal energy at the input of the filter with the signal energy at the output of the filter. If the signal energy at the input of the filter is significantly higher than the filter output (e.g., approximately three times higher depending on the SAW filter frequency response), then it is assumed that a ground signal has been received.

If a terrestrial signal is present in the adjacent channel, terrestrial signal detector 154 generates a signal to retune local oscillators 144 and 146 to downconvert the terrestrial signal. Therefore, the center frequency of the ground signal is shifted by about 2.07 MHz, and the second IF becomes 4.60 MHz. After sampling and a/D conversion, the terrestrial signal is applied to an RRC-type digital filter 148. Since the roll-off frequency (roll-off frequency) of the digital filter 148 is selected to meet the QPSK and MCM demodulation requirements, and the terrestrial and satellite signals have similar bandwidths, the digital filter passes the MCM terrestrial signal to block 156 for down-sampling prior to FFT processing at block 158. The output of the digital filter 148 is also provided to a sample switch and latch device 160 to recover the TDM signal from the QPSK modulation performed at the broadcast station. A switch 162 is then used to select an output signal from the sample switch and latch device 160 or FFT158 for further processing by a TDM demultiplexing and decoding circuit 164 and post-detection diversity combine unit 58 (fig. 4). The operation of the switch 162 is controlled by the ground signal detector 154.

Thus, terrestrial repeater bands 50 and 52 (fig. 3) in the lower portion of the frequency plan, near satellite signal bands 46 and 48, facilitate selection of either satellite signals or terrestrial signals for receiver output. Since a portion of the adjacent terrestrial signal remains in the output of the SAW filter during satellite signal reception, the comparison of signal power can be used to detect the terrestrial signal.

While certain advantageous embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.

Claims (19)

1. A receiver configured to receive broadcast signals of a first signal type and a second signal type and to select for output one of the broadcast signals of the two signal types, the receiver comprising:

a first oscillator and mixer circuit (140, 144) for downconverting said broadcast signals of said first and second signal types to a first intermediate frequency;

a first filter (138) having a center frequency corresponding to said first intermediate frequency and having a frequency response selected to pass at least a portion of said broadcast signals of said first signal type and said broadcast signals of said second signal type;

a second oscillator and mixer circuit (142, 146) for downconverting said broadcast signals of said first and second signal types to a second intermediate frequency;

a sampling and analog-to-digital conversion circuit (150, 152) for converting the broadcast signals of the first signal type and the broadcast signals of the second signal type into digital signals; and

a second filter (148) for filtering said digital signal, coupled to the output of the sampling and analog-to-digital conversion circuitry (150, 152), phase shift keying or PSK modulating said digital signal generated from said broadcast signal of said first signal type, and modulating said digital signal generated from said broadcast signal of said second signal type according to a second modulation scheme different from PSK modulation.

2. The receiver of claim 1, wherein a third filter is used in generating said broadcast signal of said first signal type, said second filter (148) being configured to have a frequency response corresponding to a matched filter of said third filter.

3. A receiver according to claim 1, said second modulation scheme being multi-carrier modulation or MCM, and said second filter (148) being configured to have a frequency response that facilitates MCM and PSK demodulation.

4. A receiver according to claim 3 wherein the frequency response accommodates a sampling frequency for MCM demodulation corresponding to at least one of the length of a fast fourier transform for MCM demodulation and the length of a guard interval used in MCM modulation.

5. The receiver of claim 1, further comprising a signal detection circuit (154) coupled to said second filter (148) for determining whether a characteristic of said second signal type exceeds a predetermined limit and for generating an output signal for controlling operation of said first oscillator and mixer circuit (140, 144), said first oscillator and mixer circuit (140, 144) being configured to generate said first intermediate frequency by mixing with a corresponding one of said first signal type and said second signal type using one of a first and a second input frequency in dependence on said output signal.

6. A receiver according to claim 1, further comprising a first signal demodulating means (160) coupled to said second filter (148) for processing said first signal type, a second signal demodulating means (156, 158) coupled to said second filter for processing said second signal type, and a switching means (162) for selecting an output of one of said first signal demodulating means (160) and said second signal demodulating means (156, 158) based on said output signal from said signal detecting means.

7. A receiver according to claim 1, wherein said second signal type is a multi-carrier modulated signal which is demodulated using a down-sampling and fast fourier transform process, said second filter (148) being configured to operate in accordance with selected filter parameters to facilitate said down-sampling and said fast fourier transform process of said second signal type and PSK demodulation of said first signal type.

8. The receiver of claim 7, wherein the second filter (148) is a root-raised-cosine filter.

9. The receiver of claim 8, wherein said second filter (148) is a matched filter configured to substantially correspond to a third filter located at a broadcast station generating said first signal type.

10. A method for receiving and selecting broadcast signals transmitted from first and second frequency channels, comprising the steps of:

receiving a signal at a carrier frequency;

down-converting said received signal to a first intermediate frequency;

filtering the received signal to deliver the broadcast signal on the first and second frequency channels;

down-converting the broadcast signal to a second intermediate frequency at the first frequency channel and the second frequency channel;

sampling the broadcast signal and converting it into a digital signal; and

filtering the digital signal, wherein the digital signal generated from the first frequency channel is phase shift keyed or PSK modulated and the filtering is performed using a root-raised cosine filter to facilitate PSK demodulation, and wherein the digital signal generated from the second frequency channel is modulated according to a second modulation scheme different from PSK modulation and wherein the filtering is performed using a root-raised cosine filter.

11. The method of claim 10, wherein said filtering step includes the step of selecting said root raised cosine filter to have a frequency response corresponding to a matched filter of a third filter for producing said broadcast signal at said first frequency channel.

12. A method according to claim 10, wherein said second modulation scheme is multi-carrier modulation or MCM, and said providing step includes the step of selecting said frequency response to facilitate MCM demodulation.

13. The method of claim 12, wherein the selecting step comprises the steps of: selecting a sampling frequency based on a sampling frequency for MCM demodulation, the sampling frequency corresponding to at least one of a length of a fast Fourier transform for MCM demodulation and a length of a guard interval used in MCM modulation.

14. The method of claim 10, wherein said broadcast signal at said second frequency channel has a higher signal level than said broadcast signal at said first frequency channel and further comprising the steps of:

comparing signal levels of said digital signal before and after said filtering step to determine if a characteristic of said broadcast signal at said second frequency channel exceeds a predetermined limit;

generating a detection signal indicating whether the broadcast signal at the second frequency channel has been detected; and

adjusting an input frequency to a local oscillator based on the detection signal to downconvert the received signal to the first intermediate frequency by mixing with the received signal in the first and second frequency channels.

15. A receiver configured to receive a first signal type signal corresponding to phase shift keying or PSK modulation and a second signal type signal corresponding to multi-carrier modulation or MCM and to select one of the two signal types for output, the receiver comprising:

a first oscillator and mixer circuit (140, 144) for downconverting said first signal type and said second signal type to a first intermediate frequency;

a first filter (138) having a center frequency corresponding to the first intermediate frequency and a frequency response selected to pass at least a portion of the first signal type and the second signal type.

A second oscillator and mixer circuit (142, 146) for downconverting the first and second signal types to a second and third intermediate frequencies, respectively;

a sampling and analog-to-digital conversion circuit (150, 152) for digitizing the first signal type and the second signal type; and

a second filter (148) coupled to an output of said sampling and analog-to-digital conversion circuit (150, 152), said second filter (148) being a raised cosine filter having a frequency response selected to facilitate demodulation of said first signal type and said second signal type.

16. The receiver of claim 15, wherein said first filter (138) is a leaky filter selected from the group consisting of a surface acoustic wave filter and a ceramic filter.

17. The receiver of claim 15, further comprising a signal detection circuit (154) coupled to said second filter (148) for determining whether a characteristic of said second signal type exceeds a predetermined limit, and for generating an output signal for controlling operation of said first oscillator and mixer circuit (140, 144) to mix with a corresponding one of said first signal type and said second signal type using one of first and second input frequencies in accordance with said output signal to generate said first intermediate frequency.

18. The receiver of claim 17, wherein the second signal type is characterized by a signal level higher than the first signal type, the signal detection circuit (154) being configured to determine a difference in the signal level of the second signal type at the input and output of the second filter (148).

19. The receiver of claim 17, further comprising a signal detection circuit (154), coupled to said second filter, for determining whether a characteristic of said second signal type exceeds a predetermined limit, and for generating an output signal if said predetermined limit is exceeded for controlling operation of said second oscillator and mixer circuit (142, 146) to control said second oscillator and mixer circuit (142, 146) to downconvert using said third intermediate frequency.