Motorola promised a demo of long-term evolution’s raw capabilities at CTIA Wireless, and it delivered. In the two weeks before the show Motorola set up two ad hoc LTE networks using its new eNode B base station and Andrew Corp antennas, its aim to give customers and applications developers a taste of how LTE would perform in real-world conditions.
Motorola demoed two versions of the same application, HD video streaming. The first demo streamed unbuffered HD live video transmitted through a 2.6 GHz LTE network at Moto’s booth on the show floor, through a packet core network and out over a 700 MHz LTE cell site mounted on the convention center’s roof. The outdoor network had two overlapping sectors, which a Moto demo truck drove back and forth between.
The video was choppy and full of artifacts at many points, especially during the hand-off between sectors. But when Moto switched to the second demo, buffered HD video streamed from a commercial Internet site, the video flowed smoothly without a hitch. Motorola senior marketing director Tom Gruba said the point of the demo was to delineate the capabilities of LTE in a raw state versus its capabilities optimized state.
As for capacity, the average bandwidth delivered over the outdoor LTE network was only about 15 Mb/s on the downlink and 10 Mb/s on the uplink over a 5 MHz-by-5Mhz split channel. Compared to the 50 Mb/s to 60 Mb/s Verizon is seeing in its trial networks, that capacity is relatively small. But Motorola officials said the lower capacity is due to the ad hoc deployment. The antennas aren’t mounted on a high tower, but on a low mast at the top of the convention center, interfering with the networks propagation—radio waves are beamed at such a low angle they’re skipping across the parking lots. The deployment is also a single antenna-single output (SISO) deployment as opposed to the multiple smart antenna systems that will be standard in commercial LTE gear. While the SISO system does cut down on capacity, Moto is using receive diversity techniques in the network allowing it take advantage of signals bouncing off nearby casinos. Also, the sectors are literally right on top of one another, overlapping in a topology no carrier would ever deploy. That results in frequent hand-overs between sectors and big dips and peaks in available capacity.
Motorola has done side-by-side comparisons between its own WiMAX gear and LTE systems, finding that an optimized LTE network is about 15% more efficient than an optimized WiMAX network, which typically supports average downlink capacities of 30 Mb/s and uplink capacities of 10 Mb/s. Though WiMAX and LTE use the same fundamental orthogonal frequency division multiplexing access (OFDMA) technology, WiMAX is now a two year old standard. Meanwhile, LTE has had the advantage of a longer development cycle to refine its radio interface.
