集成移动电视功能的手机即将到来（英文）

Currently 3G operators (such as Vodafone in the UK) are delivering mobile TV over their existing WCDMA networks using a unicast model. However, as more subscribers transition to 3G, there’s a risk that networks could become completely congested. This has lead to an active search for an alternative technology to fulfill this need and some operators have been trialing DVB-H systems as a possible solution. In addition, Qualcomm has been promoting its MediaFLO technology as a solution and already has a commitment from a U.S. operator to utilize this system.

Whilst both of these technologies meet the technical criteria of delivering mobile TV, each has commercial drawbacks for the mobile operators. Both systems require network operators to partner with third parties for use of their spectrum and also require additional physical infrastructure build-out. There are also considerable issues in relation to the spectrum available for mobile broadcasting.

Spectrum
Spectrum is the precious commodity of the 21st century. The finite amount of useful spectrum coupled with the ever increasing demand for higher user throughputs has pushed technologies that seek to exploit the available spectrum as efficiently as possible. As a consequence, less spectrally efficient technologies are being phased out and replaced with newer and more bandwidth-efficient counterparts. An example is the replacement of analog broadcast techniques in favor of digital broadcasting technologies, for both radio and television applications. However, as with many such processes, the phasing out of old technologies takes time and consequently the spectrum typically isn’t available for re-farming until years after the new technology has superseded the old.

A second consequence of the limited availability is the potentially high dollar value associated with the use of spectrum when available on the open market. This was witnessed in 2001 when the first U.K. IMT-2000 3G license auctions generated around $40 billion. As part of the spectrum bundle offered in many countries, operators obtaining 3G licenses gained access to both paired (FDD) and unpaired (TDD) frequency allocations (see the figure). This reflected the simultaneous development and standardization of both technologies within the 3GPP. Furthermore, the initial IMT-2000 unpaired spectrum allocations are, to a considerable degree, harmonized across many European and Asian countries.

A benefit of a wireless transmission technology operating in an unpaired spectrum allocation, i.e. time duplexed up- and down-link communications, is the ability to efficiently deliver asymmetrical up- and down-link data rates. This comes about by the ability to alter the switching point between the up- and down-link transmissions to account for a higher down than up-link rate. Therefore, it’s easy to conclude that the operators’ unpaired spectrum allocations are suited to deliver broadcast content to mobile subscribers.

Other benefits include harmonized spectrums over multiple geographies allowing operators to source devices at a group level with all of the related economies of scale. It also enables user roaming across territories. Unpaired spectrum is available now and many operators already own or have access to it.

Service requirements
It’s clear that the IMT-2000 unpaired spectrum allocations offer considerable potential for delivering broadcast content to mobile subscribers. However, some requirements are placed on the technology chosen to deliver the broadcast content. For instance, for the broadcast offering to work and be financially successful for the operator and/or the content provider, the service must be competitive in terms of service availability, pricing, choice, and quality with similar services offered by other technologies, such as DVB-H and MediaFLO.

In terms of service availability, a successful mobile broadcast offering must be accessible to its intended user base. This means the service must ensure a low outage probability throughout the coverage region. In addition, from a commercial perspective, it’s expected that over the coming years the mobile broadcast environment will be a competitive arena and thus any successful offering must compete with services from rival technologies. Also, users are generally less willing to pay for broadcast content than for broadband Internet access. These factors dictate that competitive mobile broadcast technologies must meet low terminal and infrastructure cost targets while achieving a low cost of content delivery or operating overhead.

Through digital satellite and terrestrial broadcasting technologies, users have come to expect a significant choice in terms of broadcast content. Despite the technological difficulties in moving from a fixed to a mobile environment, user expectation levels have been set and it’s unlikely that anything less will be tolerated. Being competitive in the mobile environment requires not only offer a similar number of high-quality broadcast channels, but also the same level of service while the in motion. To meet this expectation level, a typical spectral efficiency target for mobile broadcast technologies is 1 bit/s/Hz with a constant service level across 95% of the coverage area.

Technology
One recently announced solution combines the performance advantages of a commercial UMTS TD-CDMA solution with the newly defined Release 6 Multimedia Broadcast and Multicast Standard (MBMS) to give operators some significant strategic, performance, and economic advantages over alternative mobile TV solutions. TD-CDMA, or UTRA TDD, has been standardized through the 3GPP and provides a high level of harmonization with WCDMA (also known as UTRA FDD). This technology can be harnessed to efficiently deliver mobile broadcast content.

As part of the 3GPP standards, TD-CDMA was standardized with the IMT-2000 unpaired spectrum allocations in mind. At frequencies in the vicinity of 2 GHz, typical mobile broadcast deployments are likely to have a cellular topology, irrespective of the underlying technology implemented. For instance, it’s unrealistic to expect 100-m towers to be scattered throughout a suburban environment, each with several kilowatts of effective radiated power.

With this in mind, it makes sense to employ a standardized cellular technology to deliver mobile broadcast content in these frequency bands. While it’s feasible to employ the 3GPP UTRA FDD mode to deliver content to mobile subscribers, the technology is fundamentally symmetrical and employs dedicated signaling bearers. Thus, in addition to the technology being spectrally inefficient when significant asymmetries exist between up- and down-link traffic as the technology increases in popularity, the network will quickly become overloaded.

A key advantage of UTRA TDD is its high degree of harmonization that exists with UTRA FDD. This translates to equipment and software sharing several areas of the network infrastructure, meaning that 3G operators can reuse existing UTRA FDD cell-site equipment for UTRA TDD broadcast delivery, such as sharing of base station antenna systems. It’s also possible to share components on the end-user device, helping to maintain battery life and not significantly impact form-factors.