OpenAirInterfaceTM (OAI): Towards Open Cellular Ecosystem
Table of Contents
OpenAirInterfaceTM (OAI) wireless technology platform is a flexible platform towards an open LTE ecosystem. The platform offers an open-source software-based implementation of the LTE system spanning the full protocol stack of 3GPP standard both in E-UTRAN and EPC. It can be used to build and customize a LTE base station (OAI eNB), a user equipment (OAI UE) and a core network (OAI EPC) on a PC. The OAI eNB can be connected either to a commercial UEs or OAI UEs to test different configurations and network setups and monitor the network and mobile device in real-time. In addition, OAI UE can be connected to eNB test equipment (CMW500) and some trials have been successively run with commercial eNB in December 2016.
OAI is based on a PC hosted software radio frontend architecture. With OAI, the transceiver functionality is realized via a software radio front end connected to a host computer for processing. OAI is written in standard C for several real-time Linux variants optimized for IntelTM x86 and ARMTM processors and released as free software under the OAI License Model. OAI provides a rich development environment with a range of built-in tools such as highly realistic emulation modes, soft monitoring and debugging tools, protocol analyzer, performance profiler, and configurable logging system for all layers and channels.
Towards building an open cellular ecosystem for flexible and low-cost 4G/5G deployment and experimentations, OAI aims at the following objectives:
- Open and integrated development environment under the control of the experimenters;
- On the network side: Fully software-based network functions offering flexibility to architect, instantiate, and reconfigure the network components (at the edge, core, or cloud using the same or different addressing space);
- On UE side : Fully software-based UE functions which can be used by modem designers with upgrading and/or developing LTE and 5G advanced features
- Playground for commercial handsets as well as application, service, and content providers;
- Rapid prototyping of 3GPP compliant and non-compliant use-cases as well as new concepts towards 5G systems ranging from M2M/IoT and software-defined networking to cloud-RAN and massive MIMO.
Currently, the OAI platform includes a full software implementation of 4th generation mobile cellular systems compliant with 3GPP LTE standards in C under real-time Linux optimized for x86. At the Physical layer, it provides the following features:
- LTE release 8.6 compliant, with a subset of release 10;
- FDD and TDD configurations in 5, 10, and 20 MHz bandwidth;
- Transmission mode: 1 (SISO), and 2, 4, 5, and 6 (MIMO 2×2);
- CQI/PMI reporting;
- All DL channels are supported: PSS, SSS, PBCH, PCFICH, PHICH, PDCCH, PDSCH, PMCH;
- All UL channels are supported: PRACH, PUSCH, PUCCH, SRS, DRS;
- HARQ support (UL and DL);
- Highly optimized base band processing (including turbo decoder). With AVX2 optimization, a full software solution would fit with an average of 1×86 core per eNB instance (64QAM in downlink, 16QAM in uplink, 20MHz, SISO).
For the E-UTRAN protocol stack, it provides:
- LTE release 8.6 compliant and a subset of release 10 features;
- Implements the MAC, RLC, PDCP and RRC layers;
- protocol service for all Rel8 Channels and Rel10 eMBMS (MCH, MCCH, MTCH);
- Channel-aware proportional fair scheduling;
- Fully reconfigurable protocol stack;
- Integrity check and encryption using the AES and Sonw3G algorithms;
- Support of RRC measurement with measurement gap;
- Standard S1AP and GTP-U interfaces to the Core Network;
- IPv4 and IPv6 support.
Evolved packet core network features:
- MME, SGW, PGW and HSS implementations. OAI reuses standards compliant stacks of GTPv1u and GTPv2c application protocols from the open-source software implementa- tion of EPC called nwEPC ;
- NAS integrity and encryption using the AES and Snow3G algorithms;
- UE procedures handling: attach, authentication, service access, radio bearer establishment;
- Transparent access to the IP network (no external Serving Gateway nor PDN Gateway are necessary). Configurable access point name, IP range, DNS and E-RAB QoS;
- IPv4 and IPv6 support.
Figure 1.1 shows a schematic of the implemented LTE protocol stack in OAI. OAI can be used in the context of a rich software development environment including Aeroflex-Geisler LEON / GRLIB, RTOS either RTAI or RT-PREEMPT, Linux, GNU, Wireshark, control and monitoring tools, message and time analyser, low level logging system, traffic generator, profiling tools and soft scope. It also provide tools for protocol validation, performance evaluation and pre-deployment system test. Several interoperability tests have been successfully performed:
- OAI eNB with the commercial LTE-enabled mobile devices, namely Huawei E392, E398u-1, Bandrich 500 as well as with commercial 3rd party EPC prototypes.
- OAI-UE with test equipment CMW500 and commercial enodeB (Ericsson on com4Innov network) with commercial EPC.
OAI platform can be used in several different configurations involving commercial components to varying degrees:
- Commercial UE ↔ Commercial eNB + OAI EPC
- Commercial UE ↔ OAI eNB + Commercial EPC
- Commercial UE ↔ OAI eNB + OAI EPC
- OAI UE ↔ OAI eNB + OAI EPC
- OAI UE ↔ OAI eNB + Commercial EPC
- OAI UE ↔ Commercial eNB + Commercial EPC
OAI is designed to be agnostic to the hardware RF platforms. It can be interfaced with 3rd party SDR RF platforms without significant effort. At present, OAI officially supports the following hardware platforms.
EURECOMTM EXMIMO2: The the default software radio frontend for OAI is ExpressMIMO2 PCI Express (PCIe) board. This board features 4 high-quality RF chipsets from Lime Micro Systems (LMS6002), which are LTE-grade MIMO RF front-ends for small cell eNBs. It supports stand-alone operation at low-power levels (maximum 0 dBm transmit power per channel) simply by connecting an antenna to the board. RF equipment can be configured for both TDD or FDD operation with channel bandwidths up to 20 MHz covering a very large part of the available RF spectrum (250 MHz-3.8 GHz) and a subset of LTE MIMO transmission modes.
Apart from real-time operation of the software modem on the hardware targets described above, the full protocol stack can be run in a controlled laboratory environment for realistic system validation and performance evaluation (see Fig. 1.2) . The platform is designed to represent the behavior of the wireless access technology in a real network setting, while obeying the temporal frame parameters of the air-interface. The platform targets large-scale repeatable experimentation in a controlled laboratory environment with various realistic test-cases and can be used for integration, performance evaluation and testing.
Figure 1.3 shows the OpenAirInterfaceTM LTE eNB, EPC demonstration and its connection with COTS UE (Bandrich C500). OAI soft eNB and 1 OAI soft EPC running on the top of Intel-based PCs. The current setup uses two different physical machines to run eNB and EPC so as to take into account the delay of S1 interface. The eNB is configured for in FDD band 7, with 5MHz BW and transmission mode 1 (SISO). The OS is a low latency Linux kernel and the hardware platform is the EXMIMO 2. Fig. 1.4 shows the two screen-shots of the connection manager of the dongle. It can be observed a successful attached procedure (left figure) and downlink data rate of 7Mbps obtained (right figure).