Unsubstantiated reports from various sources reflect a mixed message relative to the technical efficacy of the ATSC Mobile/Handheld (M/H) standard in actual practice. As we know, last spring selected TV stations started extensive field testing of the system in several US markets under varying terrain, urban density and other related signal propagation parameters. Prototype receiving units (none yet marketed) from several manufacturers and in various physical configurations are, of course, an integral part of the system’s tests.
Commercial applications considerations aside, technically, M/H works as advertised. The question is: does it meet customer expectations? (Evidently), the area of most concern is the level of performance in weak signal conditions compared to that of 3G/4G “smart phone” video services.
By definition the cell phone system produces a relatively high power density, because service areas are covered by several transmit-receive locations (cells). In the traditional TV broadcast model a large area is covered by a single high-powered transmitter, the power level of which diminishes exponentially relative to the distance from the transmitter. Regardless of the amount of extra M/H coding to enhance reception robustness, a point is quickly reached at which insufficient signal exists to sustain decoding, and the picture (and sound) disappears. The relatively long decoding reacquisition time, if and when enough signal power is reacquired, only exacerbates the perceived performance issues.
Add the above considerations to the expectation that the receiver should perform equally well over a wide range of frequencies in both UHF and VHF bands further heightens the challenge. It is relatively easy to construct a high gain, resonant antenna for the UHF hand compared to the VHF band. Traditional antenna design dictates an external (to the receiver housing) rod or wire to achieve adequate VHF performance. This is not the form factor consumers are expecting in portable devices.
The question remains, notwithstanding the stated issues: is the system good enough for “prime-time?” In my opinion, it is. The U.S. market has never had truly portable, mobile TV service from their local outlets, so there really isn’t a precedent. Initially, the service will be somewhat “spotty” particularly in indoor locations, and the early receivers will include some type of external antenna. However, later generation M/H service systems will address these issues with a combination of “intelligent” diversity antennas on the receiver end and signal frequency networks and/or distributed antennas on the transmitter end.
Within five years at least 50% of all smart cell phones and vehicles sold in the U.S. will have M/H capability if deployment starts next year. In the meantime, the best should not be the enemy of the good.
Posted by Ed Milbourn, October 27, 2010 8:35 AM
About Ed MilbournAfter graduating from Purdue University with degrees in Electrical Engineering and Industrial Education in 1961 and 1963 respectively, Ed Milbourn joined the RCA Home Entertainment Division in 1963. During his thirty-eight year career with RCA (later GE and Thomson multimedia), Mr. Milbourn held the positions of Field Service Engineer, Manager of Technical Training and Manager of Sales Training. In 1987, he joined Thomson's Product Management group as Manager of Advanced Television Systems Planning, with responsibilities including Digital Television and High Definition Television Product Management. Mr. Milbourn retired from Thomson multimedia in December 2001, and is now a Consumer Electronics Industry consultant.