HK1050279A - Mobile station receiver operable for both single and multi-carrier reception - Google Patents

Description

Mobile station receiver for single carrier and multi-carrier reception operation

Technical Field

The present invention relates generally to wireless communication systems and methods, and more particularly to RF receivers capable of receiving multiple carrier frequencies (multi-carrier).

Background

Modern wireless telecommunications systems are evolving to provide high-speed packet data services to users of mobile devices. One example is the ability to provide internet access to users of mobile devices. One wireless system that is rapidly evolving towards this direction is the Time Division Multiple Access (TDMA) system known as global system for mobile communications (GSM), in particular the enhanced GSM, GPRS (general packet radio service) and EGPRS (enhanced general packet radio service) known as GSM +.

With the development of such modern wireless telecommunication systems, the demand of users for higher-speed data connections will inevitably increase. One particularly attractive technique to increase the effective data rate is to provide a wireless network with multi-carrier transmission capabilities and a corresponding multi-carrier reception functionality for wireless devices, also referred to herein as mobile stations. In this type of system, each carrier may carry a separate data stream, or different portions of a single data stream, thus effectively increasing the overall data rate received by the mobile station. For purposes of describing the present invention, a mobile station may be a hand-held or vehicle-mounted cellular telephone, a personal communication device, a Personal Digital Assistant (PDA) -type device having wireless communication capabilities, a Personal Computer (PC) having wireless communication capabilities, and other types of devices having wireless communication capabilities.

An important consideration when implementing a multi-carrier reception function in a mobile station is that it does not adversely affect the integrity, cost, power consumption and complexity of the mobile station. Another consideration is that the inclusion of multi-carrier reception capability does not compromise the receiver's ability to operate in a normal single-carrier environment.

There are several ways to provide multi-carrier reception capability. However, as will be seen below, none of these approaches provide the best solution.

It is first noted that for a number of practical reasons, it can be seen that a Direct Conversion Receiver (DCRX) is preferably used in connection with implementing a multicarrier receiver. In the DCRX method, the received RF carrier is directly down-converted to baseband, thus avoiding the generation of one or more Intermediate Frequencies (IF). With respect to DCRX, reference may be made to, for example, the following commonly assigned U.S. patents, which are hereby incorporated by reference in their entirety: U.S. patent No.6115593 to Petteri Alinikula et al entitled "cancellation of d.c. offset and Spurious AM Suppression in direct conversion receivers" (interference of d.c. offset and spectral AM Suppression in a direct conversion Receiver); kari Lehtinen, U.S. Pat. No.5983081, entitled "Method of Generating Frequencies in a Direct conversion Transceiver of a Dual-Band Radio Communication System, and Use of the Method and Apparatus in a Mobile Station" (Method of Generating Frequencies in a Direct conversion Transceiver of a Dual Band Radio Communication System, a Direct conversion Transceiver of a Dual Band Radio Communication System and the Use of the Method of and Apparatus in a Mobile Station); and U.S. Pat. No.5896562 to Jarmo Heinonen entitled "Transmitter/Receiver for transmitting and Receiving RF signals in Two Frequency Bands" (Transmitter/Receiver for transmitting and Receiving of an RF Signal in Two Frequency Bands).

The first possible multi-carrier reception technique may be referred to as analog down-conversion. In this system, a DCRX path is provided for each carrier from an in-phase (I) and quadrature (Q) mixer to an analog-to-digital converter (ADC). However, using this method requires a substantial increase in the required power consumption and circuit area, and sensitivity may also suffer. Furthermore, the frequency synthesizers required for multiple DCRX are required to operate in close proximity to each other on a frequency plane (frequency plane), thereby creating possible interference effects.

Another technique is to use a wideband RF receive filter in combination with a single analog mixer and IQ mixing that occurs after the ADC. The wideband filter is expected to reject additional channels and in-band blockers (blocks) outside the group or "bundle" of subcarrier frequencies of interest. The attenuation of these signals should be sufficient not to exceed the dynamic requirements of the ADC. This means that many higher order and very high Q filters are required (if the wideband filter is not tunable). While the use of image reject mixers may provide some assistance in rejecting the interfering channel, this approach is not practical, at least from a cost-effective implementation perspective.

Another approach to implementing a multicarrier receiver is to use an analog IQ mixer pair, a complex (as opposed to "real") analog wideband filter, and final IQ detection after the ADC. However, it can be seen that the IQ imbalance at the analog end of the receiver limits the image rejection to about 30dB, which is about twice as much as it may be needed. For additional reference to this process, see U.S. Pat. No. 4914408.

Yet another way to implement a multicarrier receiver is to use analog IQ mixer pairs, real (as opposed to "complex") analog wideband (bandpass) filters and image rejection in digital form, in combination with IQ detection after ADC. In this case, the IQ mixer pair mixes the subcarrier beam to IF, and then the analog filters of the I and Q channels are used to separate the subcarriers and their images from other interfering signals. However, in this approach, the dynamic requirements of the ADC are too stringent to provide a cost-effective implementation.

A number of related prior art can be found in the following patents: U.S. patent No.4241451 entitled "single sideband signal demodulator" to r.maixner et al; U.S. patent No.4220818 to kahn entitled "AM stereo transmitter"; haartsen, U.S. patent No.6081697 entitled "multicarrier radio system and radio transceiver implementation"; boehnke et al, european patent EP938208a1 entitled "multi-carrier transmission, compatible with existing GSM systems"; and the european patent EP715403a1 entitled "satellite tuner level" by j.

It should be kept in mind that none of these conventional approaches can exhibit the desired property of providing a high degree of coordination through a single carrier receiver architecture. This is an important consideration because in the voice mode of operation, most GSM receivers are in DCRX mode, so it should be as simple as possible to switch to multicarrier reception (data mode) and switch back to the original mode.

It can therefore be appreciated that there exists an unfeasible need to provide a multicarrier receiver that overcomes the above and other problems.

Disclosure of Invention

It is a first object and advantage of the present invention to provide an improved multicarrier receiver.

It is another object and advantage of the present invention to provide an improved multicarrier receiver for mobile stations that overcomes the above and other problems, is cost-effective to implement, and is synergistic with the use of DCRX in a single carrier reception environment.

The above and other problems are overcome, and the above objects and advantages are achieved, by methods and apparatus according to embodiments of the present invention.

According to the method for multicarrier reception, the following steps are performed: down-converting the received RF signals into in-phase (I) and quadrature (Q) channel signals, wherein each signal contains a plurality of subcarriers of low intermediate frequency (low IF) and, IF necessary, one subcarrier or single carrier is centered at 0 Hz; filtering the interference signal outside the frequency band of interest with analog low pass filters in the I and Q channels; converting the I and Q channel signals to digital representations thereof; in the case of multicarrier reception, the subcarriers, which are mirror images of each other, are separated by quadrature downmixing (quadraturedwning) the digital representations of the I and Q channel signals to baseband in the digital domain; and adding or subtracting the resulting I and Q signals in digital form to obtain one or both of the upper and lower sidebands containing the desired multi-carrier. For the case of symmetric multi-carrier reception the step of down-converting comprises the step of tuning the local oscillator to the centre frequency of a group of sub-carriers, and for the case of asymmetric multi-carrier reception the step of down-converting comprises the step of tuning the local oscillator between the median sub-carrier and its interfering adjacent channels.

In the case of multicarrier operation, the wideband analog low-pass filter is replaced by a narrower filter whose bandwidth is set by the bandwidth of the individual subcarriers and whose center frequency is a fixed or tunable frequency.

In case of single carrier reception, the receiver may operate in direct conversion or low IF mode, and changing from multi-carrier reception to single carrier reception is to perform the following steps: tuning the bandwidth of the analog baseband filter to form a single carrier bandwidth; the analog-to-digital converter bandwidth and dynamic range for single carrier reception is adjusted and wherein the digital quadrature downmix and the digital adder can be reconfigured or disabled.

In case of single carrier reception, the receiver operates in an IF mode, wherein a change from single carrier to multi-carrier reception is to perform the following steps: a bypass IF filter; tuning the bandwidth of the analog baseband filter to form a multi-carrier signal bandwidth; the analog-to-digital converter bandwidth and dynamic range for multicarrier reception is adjusted and wherein the digital quadrature down-mixing and digital adder may be activated.

After analog-to-digital conversion, the amplitude and phase imbalance between the I and Q channels is compensated to maximize the suppression of unwanted sidebands.

In the case of multicarrier reception, the receiver gain in the analog circuit is adjusted according to the power of all subcarriers, or, if the subcarrier spacing is sufficiently small, according to the power of one of the subcarriers.

According to these teachings, digital filtering provides the final selectivity of each subcarrier.

The selective filtering in the analog domain may be implemented by low-pass filtering with a wide enough bandwidth to cover the entire subcarrier bundle, or each subcarrier may have its own associated narrow-band filter so that the dynamic requirements of the analog-to-digital conversion function may be mitigated compared to the case of low-pass filters.

The disclosed multi-carrier receiving method and apparatus has the highest synergy with the conventional single carrier DCRX method.

Drawings

The above and other features of the present invention will become more apparent from the detailed description of the invention when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a simplified block diagram of a wireless communication system suitable for implementing the present invention;

fig. 2 is a frequency diagram useful in explaining the operation of a multicarrier receiver and showing symmetrical groups or beams of multicarrier at the input to the receiver ADC;

fig. 3 is a block diagram of a presently preferred embodiment of the mobile station receiver of fig. 1 having multi-carrier reception and digital cancellation capability of the image frequency from a single subcarrier perspective;

FIG. 4 is a block diagram depicting post ADC carrier selection logic in accordance with an aspect of the teachings;

fig. 5 is a frequency diagram useful in explaining the asymmetric subcarrier selection process and showing asymmetric multicarrier groups or beams at the input to the receiver ADC;

FIG. 6 is a block diagram depicting a post ADC carrier selection logic like that in FIG. 4, and FIG. 6 also illustrates digital logic that compensates for amplitude and phase imbalance between the digital I and Q signals;

FIG. 7 illustrates the power measurement and digital gain control aspects of FIG. 3 in greater detail; and

fig. 8 illustrates a technique for bypassing a single carrier IF filter to provide a multi-carrier signal path.

Detailed Description

Reference is first made to fig. 1, which illustrates a simplified block diagram of an embodiment of a wireless communication system 5 suitable for implementing the present invention. The wireless communication system 5 includes at least one Mobile Station (MS) 100. Fig. 1 also shows an exemplary network operator, for example, having: a GPRS Support Node (GSN) for connecting to a telecommunications network such as a public packet data network or PDN; at least one Base Station Controller (BSC) 40; and a plurality of Base Transceiver Stations (BTSs) 50 that transmit both physical and logical channels in a forward or downlink direction to the mobile station 100 in accordance with a predetermined air interface standard. There is also a reverse or upstream communication path from the mobile station 100 to the network operator that carries mobile originated access requests and services. For the purpose of illustrating the present invention, it is assumed that the BTS 50 has multi-carrier transmission capability.

In a preferred, but non-limiting embodiment of these teachings, the over-the-air interface standard may be consistent with any standard that allows multicarrier data transmission to the mobile station 100, such as data transmission that allows internet 70 access and web page downloads. In the presently preferred embodiment of the present invention, the air interface standard is a Time Division Multiple Access (TDMA) air interface that supports GSM or advanced GSM protocols and air interfaces, although the teachings herein are not limited to TDMA, GSM, or GSM-related wireless systems.

The network operator may also include a Message Center (MC)60 of a suitable type to receive and forward messages for the mobile station 100. Other types of messaging services may include supplementary data services and a service currently under development and referred to as Multimedia Messaging Service (MMS), in which image messages, video messages, audio messages, text messages, executable content, and the like, as well as combinations thereof, may be communicated between the network and the mobile station 100.

The mobile station 100 generally includes a Micro Control Unit (MCU)120, the MCU 120 having an output coupled to an input of a display 140, the MCU 120 having an input coupled to an output of a keyboard or keypad 160. The mobile station 100 may be a handheld radiotelephone, such as a cellular telephone or a personal communication device. The mobile station 100 may also be contained within a card or module that is connected during use to another device. For example, the mobile station 100 may be contained within a PCMCIA or similar type of card or module installed during use in a portable data processor, such as a laptop or notebook computer, or even a computer that may be worn by a user.

The MCU 120 is assumed to include or be connected to some type of memory 130, including a Read Only Memory (ROM) that stores operating programs, and a Random Access Memory (RAM) that temporarily stores required data, temporary memory, received packet data, packet data to be transmitted, and the like. A separate, removable SIM (not shown) may also be provided, for example, the SIM storing a preferred Public Land Mobile Network (PLMN) list and other subscriber related information. For purposes of illustrating the invention, it is assumed that the ROM stores a program that causes MCU 120 to execute the required software routines, layers and protocols to at least enable data reception using the multi-carrier approach in accordance with the teachings herein and to provide the user with an appropriate User Interface (UI) via display 140 and keypad 160. Although not shown here, a microphone and speaker are typically provided for the user to make voice calls in a conventional manner.

The mobile station 100 also contains a wireless section that includes a digital signal processor (180), or equivalent high speed processor or logic, and a wireless transceiver that includes a transmitter 200 and a receiver 220, both of which are connected to an antenna 240 for communication with the network operator. To tune the transceiver, at least one Local Oscillator (LO)260, such as a frequency synthesizer, is provided. Data, such as packet data, is transmitted and received through the antenna 240. The following discussion relates primarily to receiver 220, which is assumed herein to be a DCRX receiver, and to the operation of DSP180 in the presently preferred embodiment of a DCRX multicarrier receiver implemented in accordance with these teachings.

By way of introduction, these teachings of the present invention relate to a combination of DCRX and a low intermediate frequency (low-IF) receiver radio architecture, where the IF of a certain subcarrier is defined by the subcarrier spacing in the frequency plane. In the case of a low IF, the IF is assumed to be non-zero and to have a value that does not require a separate analog IF filter. From the perspective of the entire subcarrier beam, the receiver operates like a conventional DCRX and mixes groups of subcarriers around 0Hz (zero hertz). In practice, if there are an odd number of subcarriers, the receiver operates like a DCRX for the median subcarrier (in the case of symmetry). The teachings of the present invention impose no requirement on the location of multiple carriers in the frequency domain, nor on the number of multiple carriers. Thus, these teachings support symmetric and asymmetric operation. An important aspect of these teachings is the configuration of single carrier DCRX for multi-carrier reception with minimal modifications and best performance in terms of current consumption and cost effectiveness.

In symmetric operation, the local oscillator 260 is tuned to the center frequency of the group or beam (of frequencies) of subcarriers and generates in-phase (I) and quadrature (Q) signals in the IQ mixer. Thus, the subcarriers of the low IF are mirrored to each other. The separation of the subcarriers as mirror images of each other is accomplished by quadrature down-mixing to the baseband in the digital domain and adding or subtracting I and Q signals to obtain the desired upper or lower sideband. In the symmetric case, both the upper and lower sidebands of the low IF signal are detected by appropriate selection of the summation operator. Depending on the actual multi-carrier deployment, a bandpass filter with a tunable center frequency at low IF may be required in front of the ADC in order to alleviate the dynamic range requirements of the ADC. However, the presently preferred mode of operation is to provide a single low pass filter prior to the analog to digital conversion function. This is possible if there is no strong interference between the subcarriers and if the subcarriers are symmetrically located in the frequency plane. With an odd number of sub-carriers in symmetric operation, the middle carrier is directly down-converted to baseband (in analog circuitry).

In asymmetric operation, receiver LO 260 is not tuned to the center frequency of the subcarrier beam, but is tuned between the subcarrier in the middle and the interfering adjacent channel of that subcarrier. This is done to alleviate the image rejection requirements. This type of operation may be required if the adjacent channel levels are low compared to the desired signal, and if the modulation scheme employed requires a high signal-to-noise ratio (SNR).

If quadrature down-conversion is used, the negative frequencies are not reflected to the real end (in fact they are reflected to some extent, but only severely suppressed). The basic idea behind the well-known concept is that the phase relationship between I and Q is different for the desired or wanted signal (+90 °, i.e. positive frequency) and the image signal (-90 °, i.e. negative frequency), which makes it possible to distinguish between these two signals.

The subcarrier beams are mixed around the DC in the quadrature analog mixer pair. The resulting mixed-down subcarriers are as shown in fig. 2 (assuming a symmetrical case) with an exemplary 600kHz carrier spacing. As can be seen, desired or wanted subcarriers 1 and 5 and wanted subcarriers 2 and 4 are mirror pairs. The image of the desired subcarrier 3 is suppressed at the time of analog IQ mixing (DCRX operation).

Fig. 3 is a circuit diagram of the image reject receiver 220. In general, fig. 3 presents the basic concept of digitally canceling the mirror frequency. As shown generally in fig. 1, receiver 220 has an input connected to antenna 240 and an output connected to DSP 180. The signal selection unit 220A in fig. 3 may be implemented by the DSP180 or digital logic. Referring to fig. 2 and 3, if desired subcarriers 2 and 4 are at antenna 240, then DSP180 outputs data in desired subcarrier 4. Using other types of symbol configurations of adder 221, the output will be the data in the desired subcarrier 2. In the presently preferred embodiment, receiver 220 includes at least one signal selection unit 220A, which unit 220A includes an adder 221 fed by a digital multiplier 222. Digital multiplier 222 receives its inputs from I-channel and Q-channel ADCs 223A and 223B, respectively. The I and Q channels are obtained by separating the received RF signal and applying the separated signals to an I channel down-converter 224A and a Q channel down-converter 224B. Downconverter mixers 224A and 224B are driven by LO 260 through phase shifter 225. The down-converter mixers 224A and 224B are followed By Baseband (BB) filters, implemented as real Band Pass Filters (BPF) or Low Pass Filters (LPF)226A and 226B, respectively. The downconverted and filtered I and Q channel signals are applied to ADCs 223A and 223B for conversion to the digital domain and further processing.

Typically, in the pair of adders 221 located just before the DSP180, it is decided whether to select the signal appearing on the negative or positive frequency mirror pair. In fig. 3, the adder 221 is configured to select the signal at the positive frequency so that the image at the negative frequency is attenuated. Another configuration of the adder 221 adding and subtracting inputs will cause cancellation or fading of the signal at positive frequencies and select the signal at negative frequencies, as described above.

The following two results are thus directly obtained: for example, desired subcarriers 1 and 5 have a common multiplier 222, but different adders 221, with one adder pair selecting desired subcarrier 1 and suppressing desired subcarrier 5, and the other selecting desired subcarrier 5 and suppressing desired subcarrier 1.

The above-described operation of receiver 220 in accordance with these teachings is illustrated in fig. 4, wherein a plurality of signal selection units 220A, 220B and 220C are provided. Since all sub-carriers are assumed to be equal in power, the image rejection requirements remain moderate.

Note that there may be digital IQ tuning before the signal selection unit 220A to improve image rejection. This is illustrated in fig. 6, where digital logic 227 uses the values of X and Y read from memory 130 to change the phase and amplitude of the I (or Q) signal with respect to Q (or I).

The purpose of IQ tuning is to compensate for phase and/or amplitude imbalances that arise in analog circuits and thus improve image rejection. For example, compensation may be performed during production testing, where the levels of unwanted and desired sidebands are compared and measurements may be made using certain tuning parameter values read from memory. The parameter value that yields the highest suppression for the unwanted sidebands is then selected for use and stored in memory 130.

As an example, assume now that the downlink multi-carrier transmission shown in fig. 2 is initiated by the network (e.g., the mobile station changes from a voice call to a data call). The procedure for the mobile station 100 to receive multiple carriers is then as follows:

the process is as follows:

(A) the bandwidth of the baseband (BB) low pass filters 226A, 226B increases from 100kHz to 1.3 MHz. Note that since the subcarrier beam is around 0Hz, the low pass filter break frequency is thus around 1.3 MHz. Since this filter is a real filter (not a complex filter), it includes all 5 subcarriers.

(B) The oversampling ratio of the I and Q branch ADCs 223A, 223B is increased to obtain sufficient dynamic range over the 1.3MHz bandwidth, or other techniques may be used to increase the dynamic range depending on the ADC topology used.

(C) If different from the single carrier operating frequency, the synthesizer (LO 260) frequency is adjusted to the intermediate frequency of the group or bundle of subcarrier frequencies. (note that there may be only two, three, or four subcarriers with different frequency spacing.)

(D) The signal path after the ADCs 223A, 223B is modified as per fig. 4. As shown in fig. 3, each mirror pair thus goes to the same signal selection units 220A, 220B and 220C, where four multipliers 222 convert the signal to baseband, followed by four adders 221 (two per subcarrier) selecting either the lower or upper sideband.

(E) Next, other further processing is provided by the DSP180, for example, applying digital Automatic Gain Control (AGC).

Further, with respect to the DSP180, still referring to fig. 3, a digital low pass filter 182 may be provided in order to achieve a final selectivity for each subcarrier. When using multi-carrier receive operation, the DSP180 may also implement digital Power Measurement (PM) logic for measuring power in all subcarriers. In this case, a digital gain unit (DGB)186 may also be provided for independently adjusting the subcarrier powers based on the measured powers obtained by unit 186.

Fig. 7 illustrates the power measurement and digital gain control aspects of fig. 3 in more detail, and also shows an analog AGC unit 227 inserted between the mixers 224A, 224B and the low pass filters 226A, 226B. Note that in some embodiments, decimation may be provided between the low pass filter 182 and the power measurement unit 184.

Fig. 8 illustrates a technique for bypassing a single-carrier IF filter 300, IF present, to provide a multi-carrier signal path. Note that the GSM receiver is assumed to be of the DCRX type, however some implementations may provide the IF filter 300 and the mixer 302, mainly due to problems with DC offset. In this case, a switching network (SW1, SW2) may be provided to bypass the on-board IF mixer 302 and the IF filter 300. If the multi-carrier operation does not have sub-carriers around 0Hz, there is no DC offset problem in the multi-carrier mode. The illustrated circuit may be utilized as long as the IQ mixer pair 224A, 224B does not contain reactive components (i.e., has a narrow bandwidth).

As noted above, some modulation schemes require a high signal-to-noise ratio (SNR), e.g., the scheme in EGPRS referred to as the Multiple Coding Scheme (MCS)9 class, which is actually MCS-9, requires almost 30dB of SNR. Thus, if there are two MCS-9 subcarriers of equal power as a mirror pair, then approximately 45dB of image rejection is required. Although the presently preferred embodiment of the present invention employs symmetric reception in combination with IQ tuning (see fig. 6), if the required image rejection cannot be achieved by additional IQ tuning, the subcarriers may be arranged asymmetrically at the ADC223 input. This is shown in fig. 5, where the desired IF subcarrier 3 is 100kHz instead of 0kHz, meaning that its adjacent channel (adj3) is the image. This alleviates the image rejection requirements of MCS-9 to about 30 dB. Note that as described above, approximately dB of image rejection is also achieved for another channel of desired subcarrier 1, which is the image of the adjacent channel of desired subcarrier 5. Asymmetric operation also provides some other advantages, such as the absence of DC bias problems.

Using the teachings of the present invention provides a number of advantages. For example, when the image is at the same level as the desired signal (symmetric case), the image frequency rejection requirement remains moderate. Note that, according to an example, the MCS-9 mode in EGPRS requires a SNR so high that the adjacent channel is actually lower than the level of the wanted channel in the standard requirements. Thus, from an image rejection perspective, it may be advantageous to have adjacent channels as images rather than the desired channel. The process of doing this (the asymmetric case) is described above with respect to fig. 5.

Furthermore, the digital implementation employed in accordance with these teachings is less sensitive to IQ imbalance. Also, using IQ tuning as shown in fig. 6 makes it possible to increase image rejection.

Furthermore, the digital implementation of the image rejection function provides rejection of all images, i.e., those images that are not only of the desired channel but also of adjacent channels. This is not the case if for example an image reject mixer is used.

The teachings of the present invention can be implemented by increasing the baseband bandwidth, including the bandwidth of the ADCs 223A, 223B, and employing the correct mathematical operations in digital circuitry, such as the DSP180, as compared to the GSM receivers currently specified.

Relatedly, the ADC223 bandwidth is effectively halved since the signal of interest is around DC, rather than around some IF, as compared to some of the other multi-carrier methods summarized above. Furthermore, the lower the IF, the easier it is to achieve a high dynamic ADC implementation. In addition, as described above, the IQ tuning of fig. 6 may be performed before the signal selection unit in order to improve image rejection.

Although the teachings of the present invention are primarily described in the context of multi-carrier reception by the mobile station 100, it should be understood that the teachings of the present invention may also be implemented on the network side (e.g., in the BTS 50) if the mobile station 100 has multi-carrier transmission capabilities.

Thus, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope and spirit of the invention.

Claims (30)

1. A method for performing single carrier and multi-carrier reception, comprising the steps of:

downconverting a received RF signal into in-phase (I) and quadrature (Q) channel signals, wherein each channel signal contains a plurality of subcarriers at a low intermediate frequency (low IF) and one subcarrier or single carrier is centered at 0Hz, IF desired;

filtering interfering signals outside a frequency band of interest in the I and Q channels using analog filters;

converting the I and Q channel signals to digital representations thereof;

separating subcarriers that are mirror images of each other by quadrature downmixing the digital representations of the I and Q channel signals to baseband in the digital domain in the case of the multicarrier reception; and

the resulting I and Q signals are added or subtracted digitally to obtain one or both of the upper and lower sidebands containing the desired ones of the subcarriers.

2. The method of claim 1, wherein:

for the case of symmetric multi-carrier reception, said step of down-converting comprises the step of tuning a local oscillator to the center frequency of a group of sub-carriers.

3. The method of claim 1, wherein:

for the case of asymmetric multicarrier reception, said step of down-converting comprises the step of tuning the local oscillator between the median subcarrier and its interfering adjacent channels.

4. The method of claim 1, wherein:

digital filtering provides the final selectivity for each of the subcarriers.

5. The method of claim 1, wherein:

in the case of the multi-carrier operation, a wide-band analog low-pass filter is replaced by a few narrower filters, the bandwidth of which is set according to the bandwidth of the individual sub-carriers and the center frequency of which is fixed or tunable.

6. The method of claim 1, wherein:

in case of the single carrier reception, the receiver may operate in a direct conversion or low IF mode, and changing from multi-carrier reception to single carrier reception comprises the steps of: tuning an analog baseband filter bandwidth to form the single carrier bandwidth, adjusting an analog-to-digital converter bandwidth and dynamic range for single carrier reception, wherein a digital quadrature downmix and a digital summer can be reconfigured or deactivated.

7. The method of claim 6, wherein:

in case of the single carrier reception, the receiver operates in an IF mode, wherein changing from single carrier to multi-carrier reception comprises the steps of: bypassing the RF mixer and IF filter, tuning the analog baseband filter bandwidth to form the multi-carrier signal bandwidth, adjusting the analog-to-digital converter bandwidth and dynamic range for multi-carrier reception, wherein digital quadrature down-mixing and digital summer can be enabled.

8. The method of claim 1, wherein:

after analog-to-digital conversion, the amplitude and phase imbalance between the I and Q channels is compensated for to maximize unwanted sideband suppression.

9. The method of claim 1, wherein:

in the case of multicarrier reception, the receiver gain in an analog circuit is adjusted according to the power of all subcarriers, or, when the spacing of the subcarriers is sufficiently small, according to the power of one of the subcarriers.

10. The method of claim 1, wherein:

in the case of the multi-carrier reception, the receiver gain in the digital circuit is adjusted separately for each sub-carrier, or the same digital gain is provided for all sub-carriers when the sub-carrier spacing is sufficiently small.

11. A receiver for single carrier and multi-carrier reception, comprising:

a down-converter circuit for down-converting a received RF signal to in-phase (I) and quadrature (Q) channel signals, wherein each channel signal contains a plurality of sub-carriers of low intermediate frequency (low IF) and, IF desired, one sub-carrier or single carrier centered at 0 Hz;

an analog low pass filter having a tunable breakover frequency for filtering interfering signals outside the band of interest in the I and Q channels;

i and Q channel analog-to-digital converters for converting the I and Q channel signals to digital representations thereof;

an I and Q channel quadrature down-mixer for separating subcarriers that are images of each other by quadrature down-mixing the digital representations of the I and Q channel signals to a baseband in a digital domain; and

digital adder logic for selectively adding or subtracting the resulting I and Q signals to obtain one or both of upper and lower sidebands containing desired ones of the subcarriers.

12. The receiver of claim 11, wherein:

for the case of symmetric multi-carrier reception, the downconverter circuit is operated by tuning a local oscillator to the center frequency of a set of subcarriers.

13. The receiver of claim 11, wherein:

for the case of asymmetric multicarrier reception, the downconverter circuit is operated by tuning the local oscillator between the center subcarrier and its interfering adjacent channel.

14. The receiver of claim 11, wherein:

for the case of multicarrier reception, each of said analog low-pass filters is replaced by at least one narrower-bandwidth filter whose bandwidth is set according to the bandwidth of the respective subcarrier and whose center frequency is fixed or tunable.

15. The receiver of claim 11, wherein:

to accommodate single and multi-carrier reception, the corner frequency of the analog low-pass filter and the bandwidth and dynamic range of the analog-to-digital converter are both adjustable, and the digital down-mixing and adder logic can be disabled when not needed.

16. The receiver of claim 11, wherein:

to accommodate both single-carrier and multi-carrier reception, the receiver further includes a switching architecture for bypassing the RF mixer and IF filter for single-carrier reception.

17. The receiver of claim 11, further comprising:

digital logic to compensate for amplitude and phase imbalances between the digital I and Q signals.

18. The receiver of claim 11, further comprising:

digital logic for measuring subcarrier power in the case of the multicarrier reception.

19. The receiver of claim 11, wherein:

in case of multi-carrier reception, the receiver further comprises a digital gain unit for adjusting the sub-carrier power independently for each sub-carrier.

20. A mobile station comprising a receive antenna and a Digital Signal Processor (DSP), said mobile station further comprising a receiver having an input connected to said antenna and an output connected to an input of said DSP, said receiver being capable of multi-carrier reception and comprising:

a down-converter circuit for down-converting a received RF signal to in-phase (I) and quadrature (Q) channel signals, wherein each channel signal contains a plurality of sub-carriers of low intermediate frequency (low IF) and, IF desired, one sub-carrier or single carrier centered at 0 Hz;

an analog low pass filter having a tunable breakover frequency for filtering interfering signals outside the band of interest in the I and Q channels;

i and Q channel analog-to-digital converters for converting the I and Q channel signals to digital representations thereof;

an I and Q channel quadrature down-mixer for separating subcarriers that are images of each other by quadrature down-mixing the digital representations of the I and Q channel signals to a baseband in a digital domain; and

digital adder logic for selectively adding or subtracting the resulting I and Q signals to obtain one or both of upper and lower sidebands containing desired ones of the subcarriers.

21. The mobile station receiver of claim 20, wherein:

for the case of symmetric multi-carrier reception, the downconverter circuit is operated by tuning a local oscillator to the center frequency of a set of subcarriers.

22. The mobile station receiver of claim 20, wherein:

for the case of asymmetric multicarrier reception, the downconverter circuit is operated by tuning the local oscillator between the center subcarrier and its interfering adjacent channel.

23. The mobile station receiver of claim 20, wherein:

for the case of multicarrier reception, each of said analog low-pass filters is replaced by at least one narrower-bandwidth filter whose bandwidth is set according to the bandwidth of the respective subcarrier and whose center frequency is fixed or tunable.

24. The mobile station receiver of claim 20, wherein:

to accommodate single and multi-carrier reception, the corner frequency of the analog low-pass filter and the bandwidth and dynamic range of the analog-to-digital converter are both adjustable, and the digital down-mixing and adder logic can be disabled when not needed.

25. The mobile station receiver of claim 20, wherein:

to accommodate both single-carrier and multi-carrier reception, the receiver further includes a switching architecture for bypassing the RF mixer and IF filter for single-carrier reception.

26. The mobile station receiver of claim 20, further comprising:

digital logic for compensating for amplitude and phase imbalances between the digital I and Q signals.

27. The mobile station receiver of claim 20, further comprising:

digital logic for measuring power in all subcarriers in case of said multicarrier reception.

28. The mobile station receiver of claim 20, wherein:

in case of multi-carrier reception, the receiver further comprises a digital gain unit for adjusting the sub-carrier power independently for each sub-carrier.

29. A method for performing multi-carrier reception in a receiver for single-carrier reception, comprising the steps of:

downconverting a received RF signal into in-phase (I) and quadrature (Q) channel signals, wherein each channel signal contains a plurality of subcarriers at a low intermediate frequency (low IF);

converting the I and Q channel signals to digital representations thereof;

separating subcarriers that are images of each other by quadrature downmixing the digital representations of the I and Q channel signals to baseband in the digital domain; and

the resulting down-mixed digital representation of the I and Q signals is selectively added or subtracted to obtain at least one of an upper sideband and a lower sideband containing a desired one of the subcarriers.

30. The method of claim 29, wherein:

said step of down-converting the received RF signal also generates sub-carriers centred around 0 Hz.