By N.Venkatesh, Chief Wireless Architect, Redpine Signals
Redpine’s RS9110 Lite-Fi offers ultra-low power draft 802.11n connectivity to handheld devices. It implements the single-stream single-antenna modes of 802.11n, giving robust performance and extended range while being fully backward compatible with existing 802.11abg networks. RS9110 stands out in several ways. An RS9110 based design is the said to be world’s first Wi-Fi Certified 802.11n draft 2.0 SDIO card. It consumes less then 1mW of power while remaining associated with a wireless network – a specification critical for integration of WLAN into mobile handsets. The solution is also certified for WMM-PS – that enables standards compliant low power voice and video transport, and WPS, or Wi-Fi Protected Setup that greatly eases the setting up of a secure connection between the client and the wireless network’s access point.
RS9110 (Figure 1), is a mixed-signal system-on-chip (SoC) that includes an analog front-end (AFE), a baseband processor (BBP), a lower MAC in a combination of hardware and a programmable engine, a CPU subsystem built around a Redpine proprietary multi-threaded processor, a choice of host interfaces, a 32kHz oscillator for use during low-power sleep modes, and a Power Management Unit (PMU). It is available in LGA and WLCSP packages.
The Lite-Fi module for mobile devices contains, in addition to the SoC, an integrated RF transceiver with power amplifier, an EEPROM and other passive components in an extremely small packaged area of less than 100sq, mm (Figure 2).
We decided early on to develop our own processor architecture rather than adopt a third party core. We developed a multi-threaded processor from the ground up optimized for low-power wireless embedded system applications and to provide us advantages in power, area and cost. The 802.11n compliant MAC in RS9110 is implemented on this processor and is supported by hardware and firmware assists in the LMAC. The protocol function distribution between hardware and software is based on minimization of power consumption governed by silicon area, CPU clock speed, and memory accesses. The LMAC contains, apart from hardware security engines and data buffers, a 16-bit processing engine – also developed in-house – that is optimized for implementing latency-critical protocol functions in low gate-count.
Lite-Fi is designed for primary use in handheld devices, and therefore offers the SDIO, SPI, and memory-mapped host interfaces. The SDIO interface in this device, unlike those on commonly available SDIO products, supports the full 11n user-level throughput – up to 40Mbps UDP in the single-stream 11n mode. With most of the WLAN and data transfer functionality being taken care of within the device, the host processor is minimally loaded, enabling easy integration of Lite-Fi into a wide variety of mobile platforms. Additionally, the chip provides a hardware security engine for efficiently carrying out upper layer security processing required for VoIP and VPN connections, further reducing host processor load.
The Baseband Processor (BBP) in Lite-Fi is built upon Redpine’s 802.11abg technology that has successfully been integrated into commercial products by its customers. The BBP is said to outperform most currently available WLAN solutions, especially in hostile wireless environments. This is measured by feeding signals to the device distorted by standardized multipath models such as ETSI-C and obtaining packet-error-rate (PER) statistics, or by measuring throughput under such conditions. The additional performance helps bring down power consumption by enabling the transfer of data at higher rates in a given situation, minimizing active, or ‘on-air’ time. Lite-Fi also supports 802.11n modes, including the use of Space-time Block Codes (STBC), that enable transfer of data robustly at higher rates with lower overhead, consuming lesser energy.
The chip itself uses a number of advanced VLSI power save techniques including the use of multiple voltage domains and software controlled voltage scaling. The integrated PMU helps provide fine-grained power supply control over all internal functional modules as well as on the external RF transceiver. Overall minimization of power consumption in critical modes is achieved by implementing techniques at a system level – with all the necessary support for them in hardware and software.
Redpine has multiple patents granted and pending on the technological innovations incorporated into Lite-Fi - these include innovations in OFDM reception, low-power techniques and architectures, and hardware and software architectures.
Lite-Fi is integrated with an RF transceiver and a few external components into one of the smallest and lowest cost WLAN modules available today. The module provides all the features essential for supporting WLAN integration into smart handheld devices - including Bluetooth coexistence, SDIO and SPI host interfaces, fixed/mobile convergence protocol assists, integrated Power Manager, minimal requirement on host MIPS and interrupt latency, multiple frequency oscillator support, and reference drivers for popular operating systems such as Windows Mobile and Linux.
The product also offers a unique capability of enabling the addition of a SD memory card to the same slot. It handles the communication between the host and the SD memory so as to enable the host to detect the presence of WLAN and SD memory as separate devices. With this capability, RS9110 attractively fits into a single SD slot without sacrificing the capacity of the system to access SD memory. RS9110 has been integrated into a mini-SD card along with several GB of SD memory.
RS9110 is alsosaid to be the only WLAN device capable of being integrated on to a micro-SD slot while offering ultra-low power consumption. The RS9110 comes in an advanced WLCSP package with a thickness of 0.35mm, which was critical to enable 11n Wi-Fi on Micro SD form factor designs.
