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Cisco & Fujitsu Beamform Live Video

Fujitsu Microelectronics and Cisco are teaming for a multi-vendor demonstration of video streaming using mobile WiMAX with beamforming, says EE Times.

The demonstration is scheduled for WiMAX World , which takes place from September 30 in Chicago.

It will utilize Cisco’s BWX300 WiMAX base station and Fujitsu’s USB client. In the demonstration, multiple video streaming and ftp files will be wirelessly transferred between the Cisco WiMAX base station and the Fujitsu USB dongle.

In early 2008 there were seven approved profiles for Fixed WiMAX operating in 2.5 GHz, 3.5 GHz, and 5.8 (unlicensed) GHz, with both time-division duplexing (TDD) and frequency-division duplexing (FDD) supported.

For Mobile WiMAX however, there are 13 defined so far, with more planned. The frequencies currently covered are 2.3 GHz, 2.5 GHz, and 3.5 GHz, with 700 MHz planned for publication late in 2008. All Mobile WiMAX (16e) profiles to date are in licensed spectrum and use Time Division Duplex (TDD), like Wi-Fi. It’s more efficient for data but less ideal for voice (cell carriers use Frequency Division Duplex (FDD), with separate “talk” and “listen” channels.

The IEEE 802.16e-2005 Mobile WiMAX specifications define Network Reference Models, or Profiles - B and C - that define the structure and the separation of various functions.

The Access Service Network (ASN) may be composed of multiple Base Stations and Gateways. The ASN includes radio basestations, antenna systems, traffic aggregation, radio resource management, subscriber authentication, IP traffic management, and IP gateway functions.

ASN Gateways provides a link to the Connectivity Service Network (CSN) - where IP applications, services, and external networks are made available. This complex but “open” architecture was necessary to allow multiple ISPs to utilize multiple WiMAX networks. It enables roaming, hand-off, billing and other backend functions across different WiMAX networks.

Profile B puts the ASN gateway functions within each WiMAX basestation, creating what is referred to as a flat ASN.
Profile C defines an architecture wherein the ASN gateway functions are distributed between the WiMAX basestations and one or more centralized ASN gateways. The Radio Resource Management (RRM) functions reside primarily at the basestation, while IP functions (including authentication, traffic management, and gateway functions) reside at the ASN gateway. Profile C enables greater flexibility for a variety of service providers (for roaming, for example).

WiMAX products were also certified in two waves, with Wave 2 (from late 2008 on) supporting MIMO and beamforming.

There are two forms of MIMO supported by Mobile WiMAX in the wave 2 certification profiles. Called MIMO Matrix A and Matrix B. Modern WiMAX clients will automatically switch between those modes for the best connections.

MIMO Matrix A uses space-time coding (STC). It improves the reliability of data transmission by sending redundant copies of a data stream over multiple antennas. It’s slower, but more reliable.
MIMO Matrix B uses spatial multiplexing. It improves the speed of data transmission by sending two independent signals on multiple antennas. It’s faster, but at the cost of range.

Beamforming uses multiple antennas to send a focused beam to an end user, creating a high-capacity link that can be steered throughout the cell area. It can be overlaid on existing standards.

Cisco says its adaptive beamforming (adopted from pioneer Navini) and integrated MIMO enables service providers to maximize coverage, capacity, and performance with 30 to 50 percent fewer basestations than competitive offerings.

Cisco says its provides at least +6 dB of downlink gain over traditional “sector” antennas and minimizes the need for MIMO Matrix A/Space Time Coding by decreasing the size of the “uncertainty zone”, where the choice of which MIMO technique to use becomes difficult to make for the basestation.

Cisco says a coverage area with a radius of 5 km (80 km2) would require 28 cell sites and 122 basestations using MIMO-only. But a four-element beamforming solution, such as found in their Cisco BWX Mobile WiMAX solution, provides +6 dB of downlink gain, and requires only 18 cell sites and 72 basestations.

The key difference between the fixed and mobile WiMax standards is a more-efficient S-OFDM modulation scheme. S-OFDMA (Scalable orthogonal frequency division Multiple Access) can assign a subset of sub-carriers to individual users. By using different subcarriers multiple people can connect at the same time on the same frequency without interference.

The number of subcarriers can be adjusted dynamically adjusting for different bandwidths and conditions. For weaker indoor reception, a Mobile WiMax client might ratchet down automatically, using fewer (but stronger) subcarriers with rugged QPSK modulation.

The Korean WiBro standard was largely developed around Scaleable OFDMA (wikipedia). The IEEE believed the advantages of Scalable carriers and subchannels were so compelling they adopted it despite the fact that it “broke” compatibility with the original 802.16-2004 standard.

Other features of the WiMAX Scaleable-OFDMA spec (pdf) include Advanced Modulation and Coding (AMC) subchannels, which match the modulation, coding and other parameters to the conditions on the radio link, and Hybrid Automatic Repeat Request (H-ARQ), which adds forward error correction (FEC) bits. HARQ is generally implemented in hardware, rather than in software, and is available in newer Mobile WiMAX CPE chips.

The 802.16e protocol supports five types of QoS — UGS (Unsolicited grant service), rtPS (Real time polling Service), ertPS (Extended Real-time POLLING SERVICE), nrtPS (Non-real-time polling service and BE (Best effort service). WiMAX Quality of Service can be “guaranteed” since its connections are based on scheduling algorithms. Wi-Fi, by contrast, is based on contention and can not guarantee QoS if too many clients request access.

Handoff was a challenge. Cellular-based standards have the advantage of many years experience in handoff. Mobile IP, with “slow” handoff, is fine for web-browsing but not enough for decent voice. Many services require the appearance of seamless connections (VoIP, VPNs, etc). Much of the complexity (and latency) on cellular networks is from maintaining these connections across cell boundaries.

A better link margin, support for mobility, improved indoor coverage, flexible management of spectrum resources, and a wider range of terminal form factors are some of the advantages offered by 802.16e over the earlier fixed 802.16-2004 (pdf tutorial). A WiMAX Forum White Paper says adding subchannelisation, MIMO and beam forming to a base station could increase coverage from 2km to 9km, a twenty-fold increase in coverage and subscribers. Consequently, most operators are expected to “standardize” on Mobile WiMax, despite its extra cost and complexity.