ADAPTIVE RADIO RECEIVER APPARATUS

Abstract: The invention relates to an adaptive radio receiver apparatus suitable for use in a base station or a mobile telephone in a telecommunication system or a telecommunication system having radio in the local loop. The radio receiver is controllable for optimising operating parameters of the amplification circuits included in the receiver, in dependence of the traffic situation in which the receiver is located. The radio receiver in accordance with the invention utilises controllable amplifiers and adaptive control logic for controlling the operating parameters. The receiver apparatus comprises at least one controllable amplifier stage which is under control from a control unit for varying the operating parameters of the amplifier stage in dependence of the environment. The amplifier stage preferably includes a controllable low noise amplifier and a variable attenuation attenuator. Preferably the receiver apparatus has the capacity of controlling the operating parameters such as the blocking level, the intercept level, the sensitivity, the noise figure, the power consumption and the gain. The control unit comprises control logic for forming combinations of the operating parameters, each combination corresponding to a specific traffic situation.

Description: TITLE OF INVENTION: ADAPTIVE RADIO RECEIVER APPARATUS FIELD OF THE INVENTION The present invention relates to an adaptive radio .re¬ ceiver apparatus and, more specifically, a radio receiver suitable for use in a base station or a mobile telephone in a telecommunication system or a telecommunication system having radio in the local loop. The radio receiver is cόn- trollable for optimising operating parameters of the ampli¬ fication circuits included in the receiver, e.g. gain, noise figure, blocking and IP3 intercept levels, in dependence of the traffic situation in which the receiver is located. The radio receiver in accordance with the invention utilises controllable amplifiers and adaptive control logic for con¬ trolling the operating parameters. STATE OF THE ART In the base stations and mobile stations or other radio terminals of today the receiver is designed as a compromise mainly between intercept/blocking level and noise figure. This results in a quite modest performance in both respects. Thus, the problem is that a general receiver is not suitable for the various traffic situations encountered in a telecom- munication system. A solution is to make one type of base station for areas with intensive traffic, typically cities, having high intercept level and poor noise figure, and another type of base station for areas with low traffic intensity, such as rural areas, having low noise figure and low intercept level. However, this means a logistical problem, results in smaller series and consequently, higher costs. Also, the traffic situation is not stable, but the requirements may vary with time. Today, there is no technology for optimising the per- formance of the receiver with respect to the traffic environment . The present invention proposes to solve the problem stated above by providing an adaptive radio receiver appara- tus which may be optimised with respect to one or more of a plurality of operating parameters. This means that the same receiver may be used in all environments and having the best performance possible and the power consumption may also be reduced in accordance with the traffic environment. SUMMARY QF THE INVENTION The present invention provides an adaptive radio re¬ ceiver apparatus connected to an antenna, a duplex filter, a local oscillator and a mixer as is conventional in the art. In accordance with the invention, the receiver appara¬ tus comprises at least one controllable amplifier stage which is under control from a control unit for varying the operating parameters of the amplifier stage in dependence of the environment . The amplifier * stage preferably includes a controllable low noise amplifier and a variable attenuation attenuator. Preferably the receiver apparatus has the capacity of con¬ trolling the operating parameters such as the blocking level, the intercept level, the sensitivity, the noise figure, the power consumption and the gain. The control unit comprises control logic for forming combinations of the ope¬ rating parameters, each combination corresponding to a spe¬ cific traffic situation. Further embodiments of the invention are set forth in detail in the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described below with reference to the attached drawings in which, Figure 1 is a circuit diagram of a first embodiment of the invention having a frequency independent splitter, Figure 2 is a circuit diagram of another embodiment of the invention in which the signal is split into different frequency bands, and Figure 3 is a circuit diagram of an alternative em- bodiment of a controllable amplifier in accordance with the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As is mentioned above, receivers of e.g. base stations of mobile telecommunication systems have different require¬ ments in dependence of the environment in which they are to be used. Below is an example of a non-exhaustive list of common traffic cases : 1) In areas with low traffic intensity, it is desired to locate the base . stations as sparsely as possible. In this case, the best possible sensitivity is required of the re¬ ceiver. Then the receiver is to be designed such that the best possible noise figure is achieved. The amount of sig- nals received are on the other hand quite small, in which case the risk of interference or blocking is very small. 2) In a situation with high traffic load a large amount of signals is received, of which not all are interesting. The other signals may disturb the reception of the desired signal by forming intermodulation products in the receiver or because the receiver is blocked by strong undesired sig¬ nals. In this case, the receiver is to be designed such that the best possible tolerance -to undesired signals are achieved (high intercept and blocking level) . On the other hand, the reception sensitivity is not very important. 3) The requirement of low power consumption is self- evident in a battery powered mobile telephone, but is also desired e.g. in microcells or smaller, in which it is con¬ templated to power the base station by solar or wind power. Also in areas having poor infrastructure, it may be a great advantage having low power consumption. In large base sta¬ tions having many transponders the power requirement may be very large with associated cooling problems. This, too, re¬ quires a lower power consumption. 4) In some situations, it may be desirable to have the largest possible gain from the receiver. This enables a cost effective upgrading of older base stations where the re¬ ceiver has poor noise figure (typically 9 dB) and low gain instead of substituting new expensive base stations there- for. Figure 1 describes how such an adaptive radio receiver is realized in accordance with one embodiment of the inven¬ tion. The receiver is connected to an antenna through a duplex filter DPX as is conventional. The receiver comprises low noise amplifiers GI and G2 and a splitter SP1, splitting the signal such that a plurality of radio channels may be received at the same time. In the embodiment of Figure 1 the signal iε split by the splitter and then mixed into tuned receivers of which only the first mixer MIX11 is shown. In the embodiment of Figure 2, the signal is divided by a filter bank Fll, F21, F31, in which each filter corresponds to one radio channel . Reverting to Figure 1, the receiver apparatus is optimised by varying the attenuation of variable attenuators Al, A2, A3, A13 and by varying the bias of the amplifiers GI, G2, by changing the input voltages U... and input currents I.... As is described below a control unit (Multicoupler controller) controls the bias of the various components . The attenuators Al, A2, A3, A4 and A13 receive the bias voltages Ul, U4, U7, U10 and U16, respectively. The amplifier units GI, G2 and G12 receive the bias voltages U3 , U6, and Ull, respectively, as well as the bias currents II, 12 and 112, respectively. Since the input impedances of the amplifiers GI, G2 are affected by the bias there are variable matching networks Ml, M2 in front of the amplifiers Gl, G2. The matching net¬ works may be implemented e.g. by varactors or PIN diodes and are controlled by the input voltages U2 and U5. In case of high input signals the amplifiers Gl and G2 are overloaded. To prevent this, the variable attenuators Al and A2 have been introduced in front of the amplifiers. The attenuators may consist of PIN diodes and may also contain capacitive and reactive components to provide broad band characteristics and optimal work load. These may also attenuate the input signal in those cases when a current lean function mode is used, as Gl and G2 may sustain lower input power without being overloaded. The output level of G2 is measured by the directional coupler with detector DC2 and the result of the measurement is used to adjust the bias of Gl and G2 (and Ml, M2) as well as the attenuation of Al, A2. In the current lean mode the output signal of G2 will be relatively small and in that case the mixer MIX11 is not required to have a large LO power. Thereby, the gain of the buffer stage G12 may be lowered by decreasing the bias Ull, 112. In order to prevent overloading of MIX11 the signal may be attenuated in A13. In case the receiver is used together with a phase con- trolled antenna the phase shift is required to be identical in the various receivers. For this reason, a signal from an oscillator OSC is injected through the directional coupler DCI and the signal after the amplifiers is measured in the comparator C0MP1. The attenuator A4 may be used to set the right level of COMP1 such that the phase is measured cor¬ rectly, and the result of the phase measurement S5 is used to control the variable phase shifter PS using the voltage U8 such that the correct phase orientation is maintained. The table below shows four examples of various setting yielding various performance of the receiver apparatus. The values shown refers to the circuit diagram of Figure 1, the gain being the total gain of the apparatus. Case Al U3 II A2 U6 12 A3 NF IIP3 PDC Gain 1 OdB 3V 10mA OdB 5V 60mA OdB 0,6dB OdBm 330mW 26dB 2 -12dB 5V 60mA -12dB 5V 120mA -12dB 18dB 25dBm 975mW -lldB 3 OdB 3V 5mA OdB 3V 10mA OdB l,8dB -7dBm 45mW 25dB 4 OdB 3V 20mA OdB 3V 60mA OdB 1, 2dB -3dBm 240mW 29dB As may be seen from the table, the four cases are well adapted to the traffic cases mentioned above. Of course, many intermediate cases and combinations are possible in order to optimise for different conditions. In DCI, DC2, DC3 a portion of the power received is coupled to a detector measuring the strength of the strongest incoming signal. This information is supplied to a control unit, herein referenced as Multicoupler Controller. A temperature sensor may be included to optimise the bias of the transistors of the amplifiers as a function of the temperature. The signal S7 from the temperature sensor SUBSTITUTE SHEET is also supplied to the controlled unit . The temperature sensor is preferably located near the various components. The entire apparatus is controlled by the Multicoupler Controller through the various voltages and currents to the attenuators and amplifiers. The Multicoupler Controller also receives input data from a Base Site Controller BSC, the de¬ tectors DCI, DC12, DC13, and from the temperature sensor. The control unit may be a single chip processor. Also the power consumption of the amplifier G12 may be optimised using the control unit. The amplifier G12 associated with the local oscillator LOll and the mixer MIX11 is used to control the LO power to the mixer and receives an input voltage Ull and input current 112 controlled by the control unit. A high intercept level requires a high local oscillator power, contrary to other operating modes. This fact is used to optimize the LO amplifier in the same way as the other amplifiers of the receiver. Figure 2 shows another embodiment of the invention in which a filter bank comprising filters Fll, F21, F31 are set to pass certain frequencies to respective amplifier channels. The filters are set such that the two branches ■ from the splitter SP2 pass alternate channels. In this way, the pass frequencies of the filters of one branch may overlap filters of the other branch without losses since the overlap does not occur in the same physical line. Thus, con¬ tinuous channel coverage is obtained. The separate channels enable an individual setting or matching of the amplifiers of each channel. Each amplifier channel comprises similar components to the embodiment of Figure 1, for which reason they are not described again in great detail. In Figure 3 an alternative embodiment of the first amplifier Gl in Figures 1 and 2 is replaced by a number, e.g. two or four, of amplifier units connected in parallel. The amplifiers Gl, G2, G3, G4 may be switched on or off by a switch network comprising eight switches SW1 to SW8. A number of transmission lines having the length L λ/4 and the characteristic impedances Z 39, 66 or 94. The impedance values are calculated to ensure that the input impedance and output impedance of the amplifier circuit is maintained at the correct value, typically 50 Ω, irrespective of the number of activated amplifier units, as is well known in the art. When a high input level is to be handled all the ampli- fier units are enabled by controlling the switches, re¬ sulting in good tolerance to intermodulation and blocking. The noise figure is also quite good. When it is desired to reduce the power consumption the amplifiers are disconnected as is described below. Thereby, the intermodulation and blocking levels are decreased as well as the power requirement . Another advantage of this amplifier arrangement is that a redundancy is achieved in case of failure in one or several amplifier units. Four, two or one amplifier can be used at a time. The switches SW1-SW4 and SW9-SW10 together with the transmission lines TRL1-TRL7 are used to maintain match to 50 ohm inde¬ pendently of the number of amplifiers that are connected. The transformations that are mentioned in the following text are all according to established transmission line theory. The input impedance of the amplifiers G1-G4, which are 50 ohm in this example, are transformed to 30 ohm by the transmission line TRL. When one amplifier is disconnected (e.g. Gl) , SW1 connects TRLl to ground. This ground connection will trans¬ form to an open circuit at the connecting point A, and thus will have no effect on matching. The impedance seen at point A when looking into the amplifiers G1-G2 will depend on the number of amplifiers connected in parallel: 1 amplifier 30 ohm 2 amplifiers 15 ohm 4 amplifiers 7,5 ohm The switches SW9-SW10 and TRL5-TRL7 are used to trans¬ form these impedances to 50 ohm. The switches will be in the following position depending on the number of amplifiers connected: Numbers of amplifiers SW9 SW10 1 2 1 2 2 2 4 1 2 TRL6 and TRL5 are connected in parallel with TRL7, or connected to ground depending on the position of switches SW9 and SW10. When they are connected to ground, the short- circuit will be transformed to an open circuit at the other end of the transmission line. The open circuit line will not have any impact on the rest- of the circuit. When they are connected in parallel, the characteristic impedance of the resulting line is changed in the same way as when two re¬ sistors are connected in parallel. These different characte- ristic impedances are used to obtain matching to 50 ohm. While the present invention has been described in de¬ tail with respect to the disclosed embodiments, several variations and modifications of the apparatus are intended to fall within the scope of the present application as de- fined by the claims below.

Claims: CLAIMS 1. Adaptive radio receiver apparatus connected to an antenna, a duplex filter (DPX) , a local oscillator (LO) and a mixer (MIX) characterised by at least one controllable amplifier stage which is under control from a control unit for varying the operating parameters of the amplifier stage in dependence of the environment . 2. Apparatus according to claim 1, characterised in that the amplifier stage includes a controllable low noise am- plifier (G...) and a variable attenuation attenuator (A...) . 3. Apparatus according to claim 1 or 2, characterised by an output level detecting device (DC2;DC11,DC21,DC31) for detecting the signal strength from the amplifier stage and supplying the information as input data (S...) to the control unit. 4. Apparatus according to any one of the preceding claims, characterised by an oscillator (OSC) for injecting a signal before the amplifier stage, the signal being passed through the amplifier stage and then extracted and compared in a comparator (COMP1) for controlling the phase character¬ istics of the amplifier stage by means of a phase shifter (PS;PS11,PS21,PS31) . 5. Apparatus according to any one of the preceding claims, characterised by a temperature sensor (TEMP) for sensing the temperature of the apparatus and supplying the information as input data (S7;U4) to the control unit. 6. Apparatus according to any one of the preceding claims, characterised by comprising two amplifier stages for amplifying a plurality of radio channels and further com- prising a frequency independent splitter connected to ampli¬ fiers tuned to different frequencies. 7. Apparatus according to any one of claims 1 to 5, characterised by comprising two amplifier stages for ampli¬ fying a plurality of radio channels and further comprising a filter bank (F...) interposed between the amplifier stages for dividing the signal to the second amplifier stage comprising a plurality of amplifier channels, each having controllable gain, the separate amplifier channels enabling an individual setting or matching of amplifier units of each amplifier channel. 8. Apparatus according to any one of the preceding claims, characterised by a variable matching network (M...) for controlling the input impedance of the amplifier stage. 9. Apparatus according to any one of the preceding claims, characterised by a controllable amplifier (G12;G22,G32) associated with the local oscillator (LO) and the mixer for controlling the power consumption of the local oscillator amplifier by the control unit. 10. Apparatus according to any one of the preceding claims, characterised by directional couplers (DC.) as the detector units. 11. Apparatus according to any one of the preceding claims, characterised in that a controllable amplifier com¬ prises a number of amplifier units (Gl,G2,G3 ,G4) connected in parallel, wherein the operating parameters are controlled by the number of amplifier units put into operation by the control unit. 12. Apparatus according to claim 11, characterised by a switch network (SW...) for enabling the respective amplifier units and a number of transmission lines (TRL) having the length L λ/4 and characteristic impedances calculated to ensure that the input impedance and output impedance of the amplifier circuit is maintained at the correct value, irre¬ spective of the number of enabled amplifier units. 13. Apparatus according to any one of the preceding claims, characterised in that the control unit receives com¬ mand inputs from a base site controller (BSC) of a tele¬ communication system. 14. Apparatus according to any one of the preceding claims, characterised in that the controllable operating parameters are the blocking level, the intercept level, the sensitivity, the noise figure, the power consumption, and the gain. 15. Apparatus according to any one of the preceding claims, characterised in that the control unit comprises control logic for forming combinations of the operating parameters, each combination corresponding to a specific traffic situation.

Inventors: JOHNSON TORBJOERN, MALMGREN JENS, JOHNSON, TORBJOERN, MALMGREN, JENS
Applicants: JOHNSON TORBJOERN, MALMGREN JENS, RADIO DESIGN INNOVATION AB, JOHNSON, TORBJOERN, MALMGREN, JENS
Application year: 1997
Main classification: H04B1
IPC codes: H03G3, H04B1