Currently, W-CDMA service operators are not able to provide rich multimedia delivery services to a huge number of subscribers simultaneously because the dedicated radio and wired link resources are required per each subscriber. Consequently, the subscribers have to pay an expensive communication fee because of occupying the resources. Although CBS (Cell Broadcast Service) is known as an existing W-CDMA broadcasting service, it dose not enable the operators to provide rich multimedia delivery services. CBS have not had great benefits to the operators because the services are limited to non-multimedia services (weather report and area information delivery, etc.) and are not enough to attract the subscribers. Recently, television services for handheld devices are available and starting to become popular. However, these services are provided by the broadcast operators, so the mobile operators cannot earn revenue directly from the services. For the reasons, the mobile operators have looked for the efficient means by which they can provide the multimedia contents delivery services by themselves.

In that situation, MBMS (Multimedia Broadcast / Multicast Services) has been standardized in 3GPP Release 6. MBMS enables mobile operators to deliver rich multimedia contents to a huge number of subscribers by broadcasting over the radio frequencies assigned to W-CDMA. Then, the subscribers are able to enjoy rich multimedia contents such as television-like programs, video delivery services and music download services at a lower price. And, the operators are able to provide services by means of two ways; broadcasting without a subscription and multicasting available after a subscription. Moreover, the operators are able to deliver not only some existing contents provided by third parties over the mobile networks but also brand-new original programs created by themselves to the subscribers. Especially, there is a possibility to be produced entirely new types of multimedia services highly converged between communications and broadcasting by MBMS because the services over MBMS are able to use uplink channels at any time unlike the television services for handheld devices. Consequently, the future services newly enabled by MBMS have potential for great growth of revenue from the subscribers.



MBMS is designed to introduce an efficient way to deliver same multimedia content to many receivers into W-CDMA systems so that the operators are able to deliver the multimedia contents to the subscribers at a lower price. If some content is delivered to the receivers by conventional point-to-point mechanism, the required radio and wired link resources are multiplied by the factor of number of the receivers. While, the radio and wired link resources required by point-to-multipoint delivery of MBMS are drastically lower than ones required by point-to-point delivery down to same as the resources for single receiver at minimum.
Figure 1: Bearers in Release ’99

Figure 2: Bearers in MBMS

MBMS provides the efficient ways of delivery for not only streaming data (video, audio, speech, etc.) but also file data (binary data, image, text, etc.)

Multicast Mode / Broadcast Mode

MBMS has two modes for accessing the source data. One is the multicast mode that the data from one source is delivered to one multicast group. A subscriber can enjoy a service only after he joins the corresponding multicast group. This is suitable for pay-per-view or pay-per-program services such as television or video on demand. The other is the broadcast mode that the data from one source is delivered to all subscribers in the service areas. There is no service subscription procedure. This is suitable for free or low price services such as advertisement or notification (ex: electronic program guide, preview, notification from operator, disaster warning, etc.)

Figure 3: Multicast Mode / Broadcast Mode

Point-to-Multipoint / Point-to-Point Switching

RNC switches over between Point-to-Multipoint and Point-to-Point connections between Node B and UEs in multicast mode so that each Node B is required less transmission power. In that case, the RNC takes into account the residual time of data transmission and the number and the distribution of UEs in a cell. The RNC counts the number of UEs joining a service in a cell. UEs in connected mode are counted when joining and UEs in idle mode are counted by the responses to periodical notifications.
Figure 4: Point-to-Multipoint / Point-to-Point Switching

Combining

UEs are able to receive multiple radio links of common channels from different cells and combine (selective combining, soft combining or RAKE combining) them so that block error rate is reduced at cell boundary. Consequently, less transmission power of Node B is required and the cell capacity is improved.

Figure 5: Combining
MBMS Market Position

Currently, MBMS enables bit rates up to 256kbps per channel while W-CDMA unicast and the television services for handheld devices enable bit rates up to 384kbps per channel. MBMS’s bit rates will be improved in near future because the standardization of high speed MBMS towards up to 1Mbps per channel is progressing.
There are also the other differences between the television services and MBMS services. The television services have more receivers than those of MBMS services. While, MBMS services have a potential to be a highly interactive services because these are able to use uplink channels at any time unlike the television services. Moreover, MBMS have special advantages for the mobile operators. MBMS is a cost effective way to realize multimedia broadcast / multicast services over their existing W-CDMA systems and a barrier-free way to enter newly into the multimedia broadcast / multicast businesses from a regulatory point of view.

Figure 6: MBMS Market Position

3. NEC’s MBMS solution

SW upgrading

NEC’s macro and micro Node Bs are designed for evolution towards MBMS. The upgrade from before 3GPP Release 5 to MBMS will be basically a SW upgrade: the SW is remotely downloaded and activated from the center. With the introduction of the future MBMS-capable Channel Coding Card (CHC), the upgrade procedure will involve a simple software download resulting in a CAPEX and OPEX saving to the mobile operator. NEC’s MBMS solution will support low-cost entry by enabling the operators to start by simply adding a single channel card to each Node B.

NEC is just developing MBMS and its enhancement (high speed MBMS) will succeed to it later on in the near future.


4. Summary

The main advantage for a 3G operator with a W-CDMA network is the ability to move up to MBMS with relatively insignificant additional infrastructure cost but via a simple software upgrade of the existing W-CDMA network.
MBMS generates ability of W-CDMA to provide brand-new multimedia broadcast / multicast services to the subscribers at a lower price. And, MBMS increases efficiency of radio and wired link resources drastically compared to W-CDMA unicast bearers. The higher efficiency supports a greater number of users accessing the network. MBMS has potential for bringing a great growth of revenue to the operators.