Abstract: Introduces the open software communication architecture of the software radio system, proposes to build a distributed processing environment on a reconfigurable hardware platform, run software components provided by different vendors to support various services, and thus reach the system Software portability, reusability and scalability.
With the rapid development of cellular wireless personal communication system services, many wireless communication standards have emerged, such as GSM, IS95, IS54 / 136, PDC, etc. These air interfaces have their own agreed bands, modulation and demodulation mechanisms, codec methods, composite access technologies and protocols for different applications and services. It is foreseeable that in the near future, the radio communication system will surely integrate various wireless access networks into a common system structure, and realize multiple standards and services through a hardware platform. Beginning in the early 1990s, radio services are evolving from long-reliant hard-wire connections to software radios.
1 Basic idea
SDR (Software Defined Radio) provides a variety of air interfaces in software and provides flexible wireless communication methods to facilitate flexible transmission mechanisms, protocols and applications. Figure 1 shows the functional modules and standard interface point conventions of a multi-mode (multiple) SDR system, where the radio node refers to a base station or a mobile terminal. The multi-mode technology requires that people can be connected to more than one channel RF band. In Figure 1, the channel set.
figure 1
A software-defined personality includes RF bands, channel sets, air interface waveforms and related functions. The RF / channel access module provides multiple signal channels and RF frequency conversion across multiple RF frequency bands. The IF processing module includes filtering, further frequency conversion, space / time diversity processing, beamforming and related functions. The multi-mode radio generates multiple air interface waveforms, which are determined by the modem module. The information security (INFOSEC) function is becoming more and more important in wireless applications. The module mainly implements functions such as transmission security, identity authentication, and privacy protection. The coded channel bitstream output by the modem is called a black (ciphertext) bitstream in INFOSEC, and is converted into a red (plaintext) bitstream via INFOSEC. It is then processed through the protocol stack to generate network bits or source bits. The network bit is connected to the remote source through the network interface according to the network protocol; the source bit is connected to the local source through the source decoder. The function of the development support part in Figure 1 is to support the download of software targets and the insertion of new technologies [1].
The basic purpose of SDR is to use digital signal processing technology to replace the main analog signal processing. Through a smart antenna, a wideband RF device, a wideband analog-to-digital converter (ADC) and a digital-to-analog converter (DAC), a universal programmable processor is used to implement IF, baseband, and bitstream processing. Because the hardware analog circuit is replaced with reprogrammable software, the software radio can change its characteristics online by dynamically allocating RF, IF, ADC, DPS hardware and algorithms, and assigning software objects to hardware components. The technologies that support software radio reconfiguration are:
(1) Programmable gate array (FPGA) that can be reconfigured by reloading microprograms;
(2) A general-purpose processor that can be reconfigured in the instruction storage area by reloading code.
figure 2
These hardware and software related microprograms and code warehouses run on a general-purpose processor somewhere in the system, which contains an operating system with file system access to the FPGA and processor. This general-purpose processor usually also contains an interface to communicate with an external signal processing subsystem, such as a user interface or a nearby monitoring station.
2 SDR software communication architecture
The SCA (Software CommunicaTIon Architecture) specification defined by the Military Joint Strategy Radio System (JTRS) has undergone two phases of Steps 2A and Steps 2B amendments and improvements. The current version, Version 2.2, was released on the JTRS website on November 30, 2001, and was adopted by the SDR Forum as the standard for SDR.
SCA is not an implementation structure, but to establish a framework that is independent of implementation for JTPS software radio development. The SCA specification includes a main document and related appendix documents that explain the software communication architecture. The appendix document has the application environment description body (AEP) and domain description body (Domain Profile) defined by JTRS. The description body contains the protocol information. The appendix documents of the SCA specification also include the application program interface (API) for waveform configuration, service definition API, security instructions, RaTIonal UML documents, and configuration management documents.
2.1 System structure
Figure 2 is a schematic diagram of the SDR system software structure and module interface, in which CORBA ORB & Services module and OperaTIng System module use existing commercial products. The characteristics of the software structure are: maximum use of commercial products and protocols; core application and non-core applications are separated from the underlying hardware through an open layered structure; a common object request agent structure (CORBA) provides a A distributed processing environment to achieve portability, reusability and scalability of software applications. According to the bit stream segmentation, the system is divided into three sub-segments: black bus (ciphertext transmission), information security (INFOSEC) and red bus (cleartext transmission). These sub-segments are physically separated from each other, thereby ensuring the isolation between black / red and the integrity of INFOSEC. Referring to the seven-layer model of OSI, the system mainly implements the tasks of the physical layer, MAC layer and some logical link layers, and then interacts with the outside world through the I / O module.
The system consists of an operating environment (OperaTIng Environment), applications, logical devices and general software rules. OE includes core framework (CF), middleware (such as CORBA's Object Request Broker ORB) and operating system, where ORB must support minimumCORBA (Minimal CORBA) specification. CORBA's extended services, such as naming services, log services, event services, and standard events, are also part of the middleware.
2.2 Core framework IDL and application program interface (APl)
The core framework CF (Core Framework) is composed of a set of open software interfaces and description bodies, which defines the configuration information, management mechanism, and mutual communication methods of the application program components in the embedded communication system. The CF interface is defined by IDL and is divided into the following categories:
(1) Basic application program interfaces, including ports, life cycles, attribute sets, resource factories, and resources;
(2) Framework control interface, including applications, application factories, domain managers; devices and device managers;
(3) Framework service interface, including file, file system, file manager. 
Appendix C of the SCA specification describes the relationship between various interfaces in detail in the form of Rational UML. These interfaces defined by IDL and the inherited classes of these interfaces also form the application program interface (API), which is referenced by the waveform application program. CF uses CORBA structure for message passing. The standard API is very important for the flexible use of applications and the replacement of devices. It also ensures that service providers and users do not need to consider the difference between the development and use of the operating environment (OE) and programming language.
2.3 Application Environment Profile (Application EnvironmentProfile)
The SCA application environment description body (AEP) is based on the POSIX real-time application support standard (IEEE Std 1003.13-1998), and supports waveform portability, structural scalability, and commercial service period. The Operating System in Figure 2 requires that the POSIX-compliant real-time operating system (OS) should provide the functions and options specified by AEP. The CORBA object request proxy ORB, CF framework control interface, framework service interface and hardware device driver are not restricted when accessing the AEP services provided by the OS, and applications are restricted when accessing these services of the OS, and need to access the file system through the CF. Appendix B of the SCA specification details the standards related to AEP.
2.4 Domain Profile (Domain Profile)
The purpose of SDR equipment is to establish a reconfigurable platform that can run software components provided by different vendors to support the services required by users. The hardware equipment and software components constitute an SCA system domain. The SCA specification requires portable software components to provide general information and clearly define the information and delivery formats of hardware devices and software components, including the location, identification, attributes, performance, and relationships of components. These information are called domain descriptors. The domain manager is to use the component configuration information of the domain description body to start, initialize and maintain the applications installed in the SCA compatible system.
The CORBA component specification developed by the object management group OMG (Object Management Group) defines the delivery configuration process of software components in an object-oriented framework, and the delivery format uses the extended markup language XML. The convention of the SCA specification on the domain description body follows the CORBA component model principle. The domain description body uses the document type definition (DTD) format, and the document suffix is ​​".dtd". There are the following types of DTD documents defined by the SCA specification. You can also add your own DTD documents during the development process.
(1) Profile Descriptor: Provide a complete document name for the SAD, SPD, or DCD instance, and access it through the "Profile" property of the CF interface.
(2) Software Assembly Descriptor (SAD): describes the software configuration characteristics of the application / waveform and the connection characteristics of the components.
(3) Software Package Descriptor (SPD): Determine the implementation of a software component, such as processor type, operating system, execution code type, and file name.
(4) Software Component Descriptor (SCD): Describe CORBA software components and their interfaces.
(5) Device Package Descriptor (DPD): used to determine the manufacturer's information.
(6) Device Configuration Descriptor (DCD): Indicate how the component initially starts a device and finds the domain manager.
(7) Properties Descriptor File (PRF): describes the properties of software packages or device packages.
Appendix D of the SCA specification details the relevant DTD documents. The following uses DCD type documents as examples to illustrate the purpose and usage of such documents. The DTD file referenced by the DCD type document is named "deviceconfiguration. + SCA version number + .dtd", such as deviceconfiguration. 2.1. dtd. The XML document instance generated according to it usually has the extension "_DCD.xml", such as NodeI_DCD. xml. The XML document indicates the referenced DTD document in the second valid line, and the XML parser verifies the validity of the XML document according to the specified DTD document.
2.5 Security Architecture (Seeurity Architecture)
In the military system, there are special organizations to define, maintain, and study security measures. As the industry and commerce departments continue to improve the requirements for keeping corporate secrets, security functions are no longer just for the needs of JTRS, and the importance of information security (INFOSEC) processors is also increasing. Using programmable INFOSEC devices, software-defined INFOSEC can be implemented. SCA's architecture also uses programmable information security modules.
3 Reference case
3.1 A typical SDR transceiver subsystem
A typical SDR transceiver should include the following three components:
(1) RF interface module: When the signal is transmitted downstream, the RF analog signal needs to undergo frequency conversion and A / D conversion to form a broadband intermediate frequency digital signal; the reverse is true when the signal is transmitted upstream. This module is responsible for frequency conversion, analog-to-digital, and digital-to-analog conversion. The embedded processor that can run OS and ORB is not used here.
(2) Channelization and preprocessing module: This module consists of multiple FPGAs and a processor that controls these FPGAs. When the signal is transmitted downstream, the intermediate frequency digital signal is subjected to digital down conversion (DDC) to obtain a narrow-band baseband signal, while when it is transmitted upstream, the digital down conversion and up conversion (DUC) are implemented by FPGA. Each FPGA must have its own logic device, and the logic device representing the transmission module must be placed on the embedded processor of this module so that other SCA devices and applications can access this module. The device manager and device drivers and supporting software must also run on this embedded processor. It should be noted that through the CORBA bus, the processor can run any CF component, no matter where these components are instantiated in the system.
(3) Baseband processing module: This module performs modulation / demodulation and bit stream processing on baseband data to obtain user data. The load data (Payload) is sent out to the transceiver subsystem via Ethernet.
All processors must run an operating system (OS) and object request broker (ORB). The waveform application runs on a general-purpose processor.
3.2 SDR-3000 software radio transceiver
After the two phases of Step2A and Step2B research and development, Boeing, Harris, Motorola and other companies have developed their own SDR products. SDR-3000 is the latest product of Canadian Spectrum Signal Processing company's FlexComm platform. The product supports hundreds of channels for simultaneous transmission and reception, and each channel contains an independent air interface protocol. The FlexCommSDR-3000 platform supports almost all antenna interface standards and is suitable for the development and use of joint tactical wireless services (JTRS), airborne communication sites (CAN), and various cellular standard software radio systems. Its advantage lies in: on the basis of existing hardware, new upgrade versions, new applications and waveforms can be installed via wireless or network to support on-site replacement; the configured system can provide new ones without additional hardware investment Business and capacity can save a lot of costs. 
FlexComm SDR-3000 is a modular software radio transceiver structure, composed of three boards, system module interface shown in Figure 3. The radio frequency signal obtained from the antenna is converted into an intermediate frequency digital signal by a conversion module, and is sent to a software I / O module through a high-speed serial bus based on RapidIO; here the channelization function, digital down conversion DDC and other preprocessing are performed, and then The serial bus is transmitted to the baseband processing module; the load data obtained by the data transceiver subsystem is finally sent to the external subsystem via the Ethernet bus of the embedded CompactPCI packet switching backplane.
Figure 4 is a schematic diagram of the software structure of SDR-3000. VSI / Pro is a standard library of vector signal image processing provided by MPI software company. The car is compatible with the VSIPL embedded API standard and includes various general processing functions such as FIY and FIR filters. quicWave is a car developed based on VSI / Pro, used to develop waveform components. The quicComm library is used to support board-level functional functions, such as inter-processor communication, programmable FPGA and PowerPC startup, and certain I / O operations.
The hardware and software of SDR-3000 support SCA. In actual application, you can choose whether to adopt this system architecture. At present, FlexComm SDR-3000 series products do not include the service functions of the SCA core framework (CF), but the transceiver subsystem can access the CF services of other subsystems running in the system through the CORBA bus (transmitted through the Ethernet bus).
3.3 Reference implementation model on PC
With the support of the SDR Forum, the Communications Research Centre Canada developed an SCA-compliant software radio system reference implementation model. The system is based on the Linux operating system and developed using JAVA language. Detailed information can be obtained from its website http: //. ca get.
Programmable hardware technologies such as FPGA and DSP and object-oriented distributed processing technology make the realization of software radio technology possible, but its development still faces many challenges, requiring hardware developers, core framework developers, and waveform application development The joint efforts of personnel and system integration developers.
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