The present invention relates to wireless communications and, more particularly, to echo cancellers in wireless communication systems.
In telephony communication systems, e.g., wireless communication networks and public switched telephone networks (“PSTN”), undesired echo is electronically controlled to maintain acceptable quality of service levels. Echo occurs when a portion of the signals input into a communication device are “reflected” or otherwise transferred back to the user above user-perceivable thresholds. For example, unless echo is controlled, a user talking on a mobile phone may hear his own voice a short time after speaking into the handset, literally creating an echo effect. The typical sources of echo are shown in
A first source of echo is acoustic echo. In acoustic echo, a wireless unit's microphone 28 picks up sound emanated by its speaker 30, both directly and from reflection off nearby surfaces, e.g., the interior of a vehicle. This may be especially problematic with “hands-free” wireless devices. Acoustic echo may also include and/or be exacerbated by ambient noise. A second type of echo is hybrid echo. Hybrid echo occurs in the PSTN 14 as a result of signal reflections in a hybrid circuit 32 (“hybrid”). A hybrid 32 is an electronic circuit or device used to convert a four-wire PSTN circuit to a two-wire PSTN circuit. The former is used for the core of the PSTN network, for connecting local exchanges and/or long distance transmission. The latter is used to connect a local exchange to a subscriber's premises. As voice signals 34 pass from the four-wire circuit to the two-wire circuit, a portion of the signal energy is effectively reflected back on itself, creating echoed speech 36. Signal propagation and processing delays may also contribute to echo.
To counteract echo, the communication network 10 will typically include one or more embedded echo cancellers 38 positioned in the digital portion of the circuit. The echo canceller 38 uses signal processing and filtering means to remove a large percentage of the echo. For example, in a typical system the echo canceller might employ a digital adaptive filter to set up a model or characterization of the voice signal and echo passing through the echo canceller. As a voice path passes back through the cancellation system, the echo canceller compares the signal and the model to cancel echo dynamically. A non-linear processor may also be used to eliminate any remaining echo by attenuating the signal below the noise floor. Wireless units may also be configured to help with the echo cancellation process, especially in the case of acoustic echo.
In designing and implementing an echo canceller for use in a communication network 10, testing is typically required for determining that the canceller functions in an intended manner within the context of the network. It may also be necessary to test whether the echo canceller meets one or more industry standards for operation within certain parameters. Testing of embedded echo cancellers is usually performed offline, with the processor algorithm being evaluated using computer executable simulations. However, the results of such testing may not be as extensive or accurate as desired, and may not allow for the testing of an echo canceller with respect to certain standards.
An embodiment of the present invention relates to a method for testing an embedded echo canceller in a wireless network. By “embedded,” it is meant that the echo canceller is deployed in the network, e.g., at a mobile switching center or the like, for carrying out echo cancellation operations on data traffic signals (e.g., voice or other data signals) in the network. The data traffic signals are routed through the echo canceller. As the echo canceller operates on the traffic signals to remove echo signals, one or more input and/or output signals of the echo canceller are measured for gauging the performance of the echo canceller. The echo signals are introduced or caused by a hybrid unit. “Hybrid unit” refers to a hybrid circuit in a PSTN (public switched telephone network), a device for simulating the operation of a hybrid circuit, or the like. A hybrid circuit is an electronic device configured for interfacing one type of trunk line with another, e.g., a 4-wire trunk circuit and a 2-wire trunk circuit.
In another embodiment, the echo canceller is located between a radio access portion of the network and the hybrid unit. For example, the echo canceller may be deployed at a mobile switching center. Various input and output signals of the echo canceller are measured. On the upstream side of the echo canceller (by the hybrid unit), the input and output signals may be measured at a digital signal cross-connect panel (“DSX panel”) connected in parallel to the echo canceller and hybrid unit. On the downstream side of the echo canceller (on the side of the radio access portion of the network), the input and output signals of the echo canceller may be approximately measured by measuring the input and output signals at a radio access interface of the echo canceller. “Radio access interface” refers not to the direct inputs/outputs of the echo canceller, but to more easily accessible points of the signal path downstream of the echo canceller, such as a base station input/output, a mobile switching center input/output, or a vocoder input/output.
In another embodiment, the hybrid unit is a hybrid interface box connected to the upstream side of the echo canceller and controlled by an echo canceller test program. The hybrid interface box is an electronics device for simulating the operation of a hybrid circuit. In operation, the hybrid unit is controlled to generate the echo signals, which in this case are test signals simulating the operation of a hybrid circuit. The hybrid interface box and/or test program may be configured to simulate a number of different hybrid circuits, for testing the echo canceller for compliance with various standards such as G.168-2000.
In another embodiment, the hybrid interface box is initially connected to the upstream side of the echo canceller (directly or indirectly). Subsequently, an ISUP communication is established between two wireless units in such a manner that the communication is routed through the echo canceller and a loop around trunk. “ISUP” is the ISDN User Part, a communications protocol used to setup, manage, and release trunk circuits that carry voice and data between parties. The ISUP protocol specifies separate traffic and signaling/control channels, as opposed to using in-band signaling. Thus, the communication may be an ISUP communication or another type of communication having separate signaling and traffic channels. Generally speaking, a loop around trunk is a line/channel used to route a communication through the same switch. Here, the loop around trunk ensures that the communication is routed along a path allowing for access to the traffic channel portion of the communication. In particular, the communication is traced to identify at least the traffic channel portion of the communication. The traffic channel is then broken, and the hybrid interface box is controlled to inject test signals into the traffic channel, e.g., the test signals simulate a traffic signal and/or echo signal as relating to a type of hybrid circuit. Operation of the echo canceller is then gauged by measuring its input and output signals. The second mobile may be ignored. Because the traffic and signaling channels of the ISUP communication are separate, the traffic channel may be broken without terminating the communication.
The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:
With reference to
Referring back to
Typically, the echo signals 46 will be hybrid echo signals introduced by a hybrid circuit 32. (The echo canceller may also be configured to remove acoustic echo.) As noted above, the hybrid 32 is an electronic circuit or device used to convert a four-wire circuit to a two-wire circuit, e.g., in a PSTN 14. When data traffic signals 42a (e.g., voice or other data signals) encounter the hybrid circuit 32, a portion of the signal energy passes through the hybrid 32 and on to a landline telephone 26 or the like. However, a portion of the signal energy may also be “reflected” to the output of the hybrid circuit 32 as an echo signal 46. The echo signal 46 mixes with whatever traffic signals 42b originate from the upstream side of the hybrid (e.g., voice signals from the telephone 26), if any. Stated simply, the echo canceller 38 compares the original upstream traffic signal 42a to the downstream combined signal 44c (“Sin”) output from the hybrid circuit 32. Since the traffic signal 42a and the echo signal 46 are related, the echo canceller uses the traffic signal 42a to identify the echo signal 46 and remove it from the combined signal 44c.
For testing the embedded echo canceller 38, traffic signals 42a, 42b are routed through the echo canceller. This may be done in a standard manner by specifically establishing a communication that passes through the echo canceller, e.g., a phone call from a wireless unit 24 to a landline phone 26 that includes signaling or setup parameters for routing through the echo canceller. Alternatively, the traffic signals may be signals not specifically intended for testing purposes, e.g., data transmissions between two third parties that coincidentally are routed through the echo canceller. As should be appreciated, an MSC 16 will typically include a number of echo cancellers and vocoders for assigning and re-assigning to different communications as the communications are established and terminated. Since the echo cancellers are all typically the same model, it may be sufficient to set up testing for one of the cancellers at random, and to then wait for traffic signals to pass through the echo canceller. (As further explained below, the communication may be traced to in effect identify the echo canceller through which the communication is passing.) Privacy provisions may need to be taken into consideration.
During the time when traffic signals 42a, 42b are routed through the echo canceller 38; the input and output signals 44a-44d of the echo canceller 38 are measured as the echo canceller operates to remove echo signals 46 from the traffic signals. At the upstream side of the echo canceller 38, the measured signals may include an upstream output 44b (“Sout”) of the echo canceller and the downstream input signal “Sin” 44c. As mentioned, the downstream input signal Sin 44c may include a traffic portion 42b and an echo portion 46. The Sin signal 44c and the Sout signal 44b can be measured in a standard manner using a PCM (pulse code modulation) analyzer, a VF (voice frequency) meter, or the like (not shown) at a DSX (digital signal cross-connect) panel 72 connected to or otherwise a part of the MSC 16 and/or echo canceller 38. The DSX panel 72 is a device that allows for the reconfigurable connection of one digital device or line to another. A typical DSX panel includes a large number of electrical ports, each of which can be connected to a line or device. The lines or devices are connected to one another by running jumpers or patch cables between the ports. To change connections, it is simply a matter of rerouting the jumpers or patch cables, instead of hardwiring the devices or lines to one another. Oftentimes, an MSC 16 will have a DSX panel 72 as part of its standard equipment for connecting or routing trunk lines (or other devices or lines) to the MSC 16.
On the downstream side of the echo canceller, there will typically be an upstream input signal 70a (“Rin”) and a downstream output signal 70b (“eco”), between the vocoder 64 and the echo canceller 38. However, it may not be possible to physically access these points in the MSC 16 for measuring the signals. Accordingly, it is possible to approximate the Rin signal 70a and the eco signal 70b by measuring input and output signals at a radio access interface of the echo canceller. As noted above, “radio access interface” refers not to the direct inputs/outputs of the echo canceller 70a, 70b, but to more easily accessible points of the signal path downstream of the echo canceller. For example, an upstream input signal 44a (“Rin′”) of the decoder 66 and a downstream output signal 44d (“Eco′”) of the encoder 68 may be measured in a standard manner using a voice packet sniffer 74 at the base station 18 or a similar tool at the packet pipe interface. The measured signals 44a-44d can be processed, interpreted, or otherwise used to gauge the echo canceller's performance in removing echo 46 introduced by a single hybrid circuit 32. In particular, the testing will be with respect to whatever type of hybrid circuit 32 is in place on the PSTN 14.
For testing purposes, a hybrid interface box 50 (“HIB”) is attached to an upstream end of the echo canceller 38, possibly through a DSX panel 72, in a manner as further explained below. The hybrid interface box 50 is an electronics device that acts as a connection interface between the DSX panel 72 (or MSC or echo canceller) and a computer unit 78 running one or more echo canceller test programs. The HIB 50 may act solely in a connection interface capacity, or it may contain various electronics components such as configurable digital signal processors for simulating the operation of one or more hybrid circuits under the control of the echo canceller test programs. In other words, the echo canceller test programs and hybrid interface box work in a complementary and coordinated manner for simulating hybrid circuits, including the generation of delay, gain/loss, filters, and external signals for double-talk. The computer unit 78 may be a standard laptop computer or other microprocessor based unit. A suitable hybrid interface box 50 and suitable echo canceller test programs may be obtained from GL Communications Inc. of Gaithersburg, Md. (www.gl.com). For example, the hybrid interface box 50 may be the GL Communications “Laptop Portable USB T1/E1 Analyzer” operating under the control of the GL Communications “Manual Test Suite” for testing compliance of echo cancellers with G.168.
Once the HIB 50 and computer unit 78 are connected to the DSX panel 72, an ISUP communication or trunk 52 is established from a first wireless unit 54a to a second wireless unit 54b through the echo canceller 38 and a loop around trunk 56. “ISUP” is the ISDN User Part, a communications protocol used to setup, manage, and release trunk circuits that carry voice and data between parties in a communication network. The ISUP protocol specifies separate traffic and signaling/control channels 58, 60, as opposed to using in-band signaling. In other words, in an ISUP communication 52 there is a separate traffic channel 58 and a separate signaling channel 60. Control signals are not embedded or otherwise transmitted in the traffic channel. The ISUP communication 52 may be grown (established) by specifying the use of ISUP in a wireless unit subscriber form. To elaborate, when establishing a communication/link from one wireless unit to another, it is possible for many different types of communications to be grown, depending on the configuration of the network 12. Thus, it is typically possible for the user to designate which type of communication is to be established by way of a wireless unit subscriber form. When the user initiates a communication (e.g., by activating the wireless unit and entering a phone number), the wireless network accesses the form, identifies which type of communication the user has designated, and automatically grows the requested type of communication in a standard manner. As should be appreciated, instead of an ISUP communication, another type of communication having separate traffic and signaling channels may be used, depending on the type and configuration of the network and the components therein.
As noted, the communication 52 is established or routed through the loop around trunk 56. The loop around trunk 56 is a line or channel used to route a communication through the same switch. In other words, where a wireless unit-to-landline phone communication would route the communication out of the MSC 16 and to the PSTN 14, with a loop around trunk a wireless-to-wireless communication is routed “out and back” through the same MSC 16. As shown in
Once the ISUP communication 52 is established, the communication is traced in a standard manner. In effect, the trace is carried out to identify the communication 52. For example, in some networks or MSC's different communications are routed through the same ports 82 and loop around trunk 56 in a time-multiplexed manner. In such a case, the trace is used to identify the time slot of the desired communication. Alternatively, the communication may be automatically randomly assigned to a dedicated loop around trunk and associated ports 80. In such a case, the trace is used to identify the MSC ports 82 (accessible by way of the DSX panel 72) through which the communication is being routed by the MSC. If the exact path or timing of the communication is known and/or pre-established, it may not be necessary to carry out the trace operation.
If it is necessary to identify the particular ports and/or loop around trunk through which the communication 52 is routed, the HIB 50 may be attached to the DSX panel 72 at that time. Otherwise, if the ports are known, the HIB 50 may be attached ahead of time, e.g., in parallel to the existing connection of the loop around trunk.
Referring to
Once the traffic channel 58 is broken to the second wireless unit 54b, the traffic channel in effect resides between the first wireless unit 54a and the HIB 50 through the echo canceller 38. Subsequently, the echo canceller test programs on the computer unit 78 are used to control the HIB 50 for injecting test signals 62 into the traffic channel 58. For example, the HIB 50 and test programs may be configured to: i) read incoming traffic signals from the wireless unit 54a (e.g., transmitted over the Tx port 84b and received at the pins 98c, 98d); ii) generate a signal 44c simulating data traffic and/or the echo signal produced by a particular type of hybrid circuit (the echo signal would be based on the incoming traffic signal); and iii) transmit the signal 44c back over pins 98a, 98b for reception at the Rx port 84a. The test signals 62 are subsequently routed to and through the echo canceller 38, and the operation of the echo canceller 38 is measured as described above with reference to
Since certain changes may be made in the above-described method and system for testing an embedded echo canceller in a wireless network, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.