Abstract:
A transceiver for a cellular telephone network includes a transmitter and a receiver that receives transmitted signals, as well as a receiver. A spectral analyzer analyzes the received signals and a controller coupled to the spectral analyzer controls the transmitter and receiver as a function of the spectral analyzer analysis.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/788,969 (entitled TRANSCEIVER OPTIMIZATION UTILIZING DIGITAL SPECTRUM ANALYZER, filed Apr. 4, 2006) which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Transceivers, such as transceivers in cellular base stations and other devices that transmit electromagnetic signals contain transmitters that amplify and transmit input signals. Amplification on an input signal is performed with a power amplifier. Power amplifiers are generally non-linear for different frequency signals. In other words, they may amplify signals at different frequencies or amplitudes with different gain. To help solve this problem, the input signal may be pre-distorted if the non-linear gain of the power amplifier is known. This helps ensure that that the output of the power amplifier is generally linear. Te effectively provide transmit signal predistortion, the output signal of a transmitter power amplifier may be fed back to the transceiver using a feedback or observation receiver. Besides feedback receivers, the transceiver may comprise main signal receivers connected to antennas. Any of the receivers may be subjected to unwanted interferences or performance degradations due to internal or external hardware impacting factors. 
     In some instances, the gain of the power amplifier may vary further under different operating conditions, such as different temperatures. The pre-distorted input signal may not be able to account for changing performance of the power amplifier. In some cases, the power amplifier may be inefficient and may also be over specified to ensure sufficient broadcasting power to obtain desired coverage. During operation, some of the following receiver parameters can adversely affect the transceiver usage: Noise-floor, spurious emissions, selectivity, or nonlinearity. The main receivers may also impair the network-level performance of a given transceiver being a part of a cellular base station in terms of cell-radius (sensitivity) and/or link capacity due to increased receiver noise-floor or interference at the receiver input. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a transceiver system with a spectrum analyzer according to an example embodiment. 
         FIG. 2  is a detailed block diagram of a transceiver system with a spectrum analyzer according to an example embodiment. 
         FIG. 3  is a block diagram of a transmitter section portion of a transceiver system according to an example embodiment. 
         FIG. 4  is a detailed block diagram of a main receiver section of a transceiver system according to an example embodiment. 
         FIG. 5  is a block diagram of a digital spectrum analyzer for a transceiver system according to an example embodiment. 
         FIG. 6  is a block diagram of a spectrum analyzer channel for a transceiver system according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims. 
     The functions or algorithms described herein are implemented in software or a combination of software and human implemented procedures in one embodiment. The software may consist of computer executable instructions stored on computer readable media such as memory or other type of storage devices. The term “computer readable media” is also used to represent any means by which the computer readable instructions may be received by the computer, such as by different forms of wireless transmissions. Further, such functions correspond to modules, which are software, hardware, firmware or any combination thereof. Multiple functions are performed in one or more modules as desired, and the embodiments described are merely examples. The software may be executed on a digital signal processor, FPGA, ASIC, microprocessor, or other type of processor operating on a computer system, such as a personal computer, server or other computer system. 
     Several embodiments are described, including the use of a digital spectrum analyzer to improve performance and increase efficiency of a signal transceiver system. The digital spectrum analyzer provides a spectral analysis of signals within a system, which in one embodiment are used to improve transceiver efficiency and avoid over-specification. 
     A digital spectrum analyzer can be used to improve performance and increase efficiency of a signal transceiver system  100  as shown in  FIG. 1 . System  100  is shown in simplified block diagram form. A digital input signal of signals to be transmitted is provided to a waveform conditioning module  115 . The waveform conditioning module  115  pre-distorts the input signal and provides it to a transmitter  120 . The pre-distortion is performed to at least partially account for non-linearity of the transmitter, such as a power amplifier. In other words the signal provided to the transmitter  120  is predistorted to help ensure that an output signal  125  provided by the transmitter  120  is closer to that desired for a given input signal given an imperfect transmitter. 
     In one embodiment, the output signal is received by a feedback receiver  130 , and provided to a spectrum analyzer  135 . Spectrum analyzer  135  also receives the input signal  110  in one embodiment, and compares the two signals to generate information about the spectral power of the two signals. The information is provided to a controller  140 , which may be coupled to the waveform conditioning module  115  for further predistortion of the input signal, and may also be coupled to the transmitter to provide gain control and/or power supply voltage control to ensure that signals are properly amplified by the transmitter. 
     Further detail of a signal transceiver system is shown at  200  in  FIG. 2 . In one embodiment, an intelligent controller  205  may be used in conjunction with a digital spectrum analyzer  210  to increase transmitter  215  efficiency and reduce unwanted spectral emissions by adjusting certain controls within digital signal generation and conditioning circuitry  220  that receives an input signal from a modem  222 . Specifically, spectral analysis measurements can be used to adjust controls in peak-envelope reduction and digital pre-distortion functional blocks within the transmit waveform conditioner  220 . 
     In transmitter architectures that employ feedback or “observation” receivers  225 , the digital spectrum analyzer can also be used with an optional analog power detector  230  to provide accurate measurements of absolute and relative spectral emissions at the output  235 . These measurements can be used by the intelligent controller  205  to increase transmitter  215  efficiency by reducing the power supply voltage to a power amplifier  240  until spectral emissions reach a maximum limit. Over-specification of the power amplifier (due to output power detector inaccuracy and erring on the side of higher power) can also be avoided by measuring spectral emissions and reducing transmitter gain only if spectral emissions are above maximum limits. 
     In a main receiver  245 , the digital spectrum analyzer  210  can be used on signals within a receive waveform conditioner  255  to measure the performance of the analog hardware indicated by broken line  250 . In particular, the spectrum analyzer  210  can be used to measure: (1) noise-floor, (2) spurious emissions, (3) selectivity, and (4) nonlinearity of the analog receiver. As well, the spectrum analyzer can be used to perform network-level performance measurements of the receive communication link such as: (1) estimation of sensitivity and capacity limits due to receiver noise-floor, and (2) detection of interferers at the receiver input. 
     Transmit waveform conditioner  220  contains blocks which perform per-carrier, composite (multi-carrier), and pre-distortion digital signal processing as shown in  FIG. 3 . Per-carrier signal processing blocks  310 ,  315  and  320  may perform functions such as rate-changing, filtering, gain control, and frequency translation. While only three such per-carrier signal processing blocks are shown, there may be many more if more than three carriers are present. A composite signal processing block  325  may perform functions such as rate-changing, peak-power reduction, filtering, and gain control. A digital pre-distortion block  330  contains algorithms for performing the inverse of the power amplifier nonlinear distortion characteristic. To improve transmitter performance and efficiency, the digital spectrum analyzer  210  can perform real-time spectral measurements on any digital waveform signal in the transmit waveform conditioner including the following:
         Composite Signal Processing Input   Composite Signal Processing Output   Predistortion Input   Predistortion Output   Feedback Signal   Predistortion Error Signal       

     The receive waveform conditioner  255  contains blocks which perform impairment compensation  410 , composite (mulit-carrier)  415 , and per-carrier digital signal processing  420 ,  425 ,  430  as shown in  FIG. 4 . While only three such per-carrier digital signal processing blocks are shown, there may be many more if more than three carriers are present. The impairment compensation signal processing block  410  may compensate for analog receiver impairments such as IQ imbalance, DC offset, and nonlinearity. The composite signal processing block  415  may perform functions such as filtering, rate-changing, and gain control. The per-carrier signal processing block  420 ,  425 ,  430  may perform functions such as frequency translation, filtering, rate-changing and gain control. To improve receiver performance and efficiency, the digital spectrum analyzer  210  can perform real-time spectral measurements on any digital waveform signal in the receive waveform conditioner including the following:
         Impairment Compensation Input   Impairment Compensation Output   Composite Signal Processing Output   Per-Carrier Signal Processing Outputs       

     The intelligent controller  205  improves transmitter performance and efficiency by performing measurements using the spectrum analyzer  210  and making appropriate adjustments to controls in the transmit waveform conditioner  220  and analog transmitter  215 . The controller  205  can have multiple and concurrent modes of operation for improving specific measures of performance. For example, a power supply unit (PSU) control algorithm can be used to reduce the average power consumption of the power amplifier  240  while guaranteeing compliance to conducted spurious emissions requirements. This algorithm would continuously repeat the following procedure:
         1. Obtain spectral measurement at Frequency Offset(s)   2. If (spectral measurement&lt;Lower Threshold) then decrease PSU voltage   3. If (spectral measurement&gt;Upper Threshold) then increase PSU voltage       

     In the procedure above, the Frequency Offset(s) and the two thresholds (Upper and Lower), which provide hysteresis, are determined by the relevant regulatory and air interface standards for the transmitter  215 . In another operating mode, the over-specification of the power amplifier  240  due to output power detector  230  inaccuracy can be avoided by having the controller  205  reduce the transmitter gain when spectral emissions are above maximum limits and the PSU is at maximum voltage. This algorithm would continuously repeat the following procedure:
         1. Obtain spectral measurement at Frequency Offset(s)   2. If PSU voltage at maximum then
           if (spectral measurement&gt;Threshold) then
               decrease transmitter gain   
               
               

     A digital device such as an FPGA, ASIC, or microprocessor can be used to implement the digital spectrum analyzer  210  in one embodiment. Two example embodiments of a flexible and logic-efficient spectrum analyzer  210  are shown in  FIGS. 5 and 6 . The digital spectrum analyzer  210  can be constructed using several spectrum analysis channels  510 ,  515 ,  520 , three of which are shown in  FIG. 5 . The multiple spectrum analysis channels  510 ,  515 ,  520  can be used to monitor spectral emissions at several frequency offsets simultaneously, which is beneficial for transmitters that must adhere to spectral emissions limits at several different frequencies as prescribed by relevant regulatory standards. 
     A spectrum analyzer channel, such as channel  510 , may be implemented as a mixer-based, flexible spectrum analyzer as shown in  FIG. 6 . This architecture represents the digital-equivalent of a heterodyne-based spectrum analyzer which is often implemented in analog hardware in modern test equipment. The digital implementation of the analog spectrum analyzer architecture is found to be optimal for laying the foundations of an adaptive digital system for transceiver monitoring and control. An input multiplexer  610  allows various signals  615  from within the digital device to be measured. A multiplier-based mixer  620  with a reset-able and programmable numerically controlled oscillator (NCO)  625  is used to provide a frequency offset to the input digital signal  615 . A resolution bandwidth filter stage  630  is used to limit spectral bandwidth of a subsequent power measurement. The resolution bandwidth filter  630  can be made programmable so that different spectral bandwidths can be configured for a specific measurement. The resolution bandwidth filter does not have stringent phase response requirements therefore it can be implemented using an efficient digital structure (such as for example an infinite impulse response (IIR) filter). A variable gain device  635  may be used to scale the digital signal to an appropriate level based on the dynamic range of a digital power detector  640 . The digital power detector  640  is used to calculate the instantaneous power of the signal envelope, and an output filter  645  is used to perform power-averaging before a spectral power reading  650  is made available to various control or monitoring devices in the system. The flexibility of spectrum analyzer configuration (ie. input signal, frequency offset, resolution bandwidth, detector signal level) allows one instance of the spectrum analyzer channel to be shared, in a time-multiplexed manner, amongst various monitoring functions in the system. This implementation of a spectrum analyzer may be implemented with much less digital logic than more well-known FFT based methods. 
     Various embodiments of the transceiver system may enable fast and effective transmit signal optimization. Optimization of peak-envelope reduction algorithms by real-time measurement of transmit signal spectrum, and optimization of pre-distortion algorithms by real-time measurement of transmit signal spectrum may be performed. 
     Real-time transmitter control for increased transmitter efficiency may be obtained due to lower power supply consumption by real-time measurement of transmit signal spectrum. This may eliminate the need for over-specification of power amplifier by real-time measurement of transmit signal spectrum. Continuous improvement of receiver performance and monitoring during operation may be obtained by measuring receiver noise-floor. Spurious signals from receiver hardware as well as interferers in receiver input spectrum, receiver selectivity and receiver linearity may be enabled. 
     Flexible spectrum analyzer configuration is provided by a programmable input signal, frequency offset, resolution bandwidth, and dynamic range. In one embodiment, one structure may be shared amongst various optimization targets. Efficient spectrum analyzer implementation may include measurement of spectral power at one frequency offset and efficient digital logic implementation. Use of envelope power detection and relaxed phase response requirements of the resolution bandwidth filter may also provide resource-efficient realizations such as infinite-impulse response (IIR) filters. In a further embodiment, one structure may provide spectral analysis with increasingly narrower resolution bandwidth for the same amount of computational complexity, while preserving optimization methods that may be implemented. Over-specification of power amplifier may be avoided by measuring output spectral characteristics. Varying power supply voltage and/or amplifier gain enables the output frequency characteristic to be within an acceptable margin of a desired frequency mask. In further embodiments, the optimization methods may be applied to improve the performance, efficiency and size of signal transceivers in different fields such as, but not limited to, RF transmission, Hi-Fi audio, Hi-Fi video, optical transmission and, generally, in systems where high-quality of electrical/electro-mechanical/electro-optical/electro-magnetic signal transmission and reception has to be achieved. 
     In various embodiments, the system  100  may reduce transceiver inefficiency and over-specification by employing spectral analysis of signals within a system composed of a signal transmitter and receiver. The cost of transmitters may be reduced by digital waveform conditioning algorithms. These algorithms are enhanced by spectral analysis of internal digital waveforms and the transmitted output spectrum. Operating voltage and output power of the transmitter power amplifier may be optimized using spectral measurements of the output transmit signal using a feedback (or observation) receiver. In the main and feedback receivers, the digital spectrum analyzer can be used to detect unwanted interferers and measure performance of the receiver analog hardware. All this may be achieved by a resource-efficient digital spectrum analyzer architecture, which need not involve computationally expensive approaches such as fast Fourier transforms (also known as FFT), and an intelligent resource-managing controller paired with it. The controller intelligence may be provided by a finite state machine responsible for specifying the generic spectrum analyzer (SA) configuration for a given transceiver application. In further embodiments, general purpose computers or programmable logic arrays or other devices capable of performing the functions described may be used. 
     The Abstract is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.