The handoff control scheme for computing powerless devices and its applications in the digital home network☆
Introduction
The radical development and evolution of wireless communication techniques enable users to enjoy multimedia services without wired connection. Typically, users can listen to audio files using devices with or without computing capability. For example, a user can listen to audio files from his PDA and Smart Phone. On the other way, a user also can listen to audio files using a light-weight Bluetooth headset (henceforth referred to simply as LW-BT headset). Since the LW-BT headset consumes less power and is cheaper than PDA and Smart Phone, it is more applicable for audio applications in the home network environment. Users in the home may still need to use the LW-BT headset to listen to audio files, because they don’t want to bother other members.
Referring to Fig. 1, the main compositions in the digital home network can be (1) a home gateway, (2) media servers (MS), (3) wireless access points (APs), (4) BT gateways (BTGW) and (5) a LW-BT headset. Audio files are distributed in media servers. Media servers share the audio files’ information with the home gateway. A user, who is equipped with the LW-BT headset, can access audio files of media servers in the home network by connecting to the home gateway. Audio files are streamed to the LW-BT headset through the BT gateway which interconnects the IP and Bluetooth networks. As a result, he can listen to audio files stored in media servers using the LW-BT headsets.
However, handoff occurs when the LW-BT headset moves out of the BT gateway’s coverage. Considering the following scenario, a housewife gets used to listen to music using a LW-BT headset when she is doing her housework. She and the LW-BT headset may roam anywhere inside the house, such as cleans a particular room and then washes some clothes on the balcony. However, the above scenario emerges the handoff issue for the LW-BT headset. The LW-BT headset doesn’t have extra computing capability, communication resource and buffer to tackle the handoff problem. Audio data would be lost when the above situation happens.
Most of current handoff control schemes are for client devices that have computing capability, e.g., Notebook, PDA and Smart Phone. Few researches consider how to achieve handoff for computing powerless client devices, such as the LW-BT headset. The LW-BT headset which is dedicated for audio applications is limited in (i) computation and (ii) communication. The power consumption consideration leads to the computing limitation, such that the LW-BT headset can only be dedicated for single purpose application, i.e., high quality audio streaming. Moreover, the LW-BT headset can only wait for connection request from the master BT device. Thus, only the mater device can connect to the LW-BT headset actively. For high quality audio applications, the LW-BT headset can only have exact one connection with the master BT device. The number of communication links for audio streaming with other mater Bluetooth devices is limited.
These limitations make existing handoff control schemes, which are for client devices with computation capability, inapplicable for computing powerless devices, such as the LW-BT headset. Some of the currently existing handoff control scheme needs BT devices with computing capability [1], [2]; some of them only consider the baseband handoff and can not be applied for high quality audio applications [3], [4].
As depicted in Fig. 2, a high quality audio application relies on the Audio/Video Distribution Transport Protocol (AVDTP) as the underlying transport mechanism for streaming audio. AVDTP relies on Logical Link Control and Adaptation Protocol (L2CAP) that provides connection-oriented communication. That is, to have an audio application, the LW-BT headset and the BT gateway must establish AVDTP, L2CAP and baseband connection with each other. Once the baseband connection is disconnected or changed due to handoff, the corresponding AVDTP would be disconnected and must be restored.
In order to deal with the aforementioned concerns, we propose Computing Powerless Handoff (CP-Handoff) for those client devices that are computing powerless in this paper. The idea of the CP-Handoff is that the handoff is triggered and handled by the master BT device. The handoff computing overhead is put on the master BT device and media servers. The slave BT device is unaware about the whole handoff process. This design is suitable for the LW-BT headset, because the CP-Handoff doesn’t need any computation on the slave BT device, i.e., the LW-BT headset. With the CP-Handoff for the LW-BT headset, one can listen to audio files anywhere in the home network.
In order to let users access audio files anytime and anywhere in the UPnP home network, we propose Ubiquitous Audio Access Platform (UAAP) in this paper. UAAP allows a user to listen to audio files, anywhere in the home environment using a LW-BT headset. In addition, audio files can be distributed in media servers that can be Desktop PCs, Notebooks, etc. The home gateway is responsible for the audio files management. A user can use devices with browsers to configure his playlist through the home gateway. When the user roams, media servers redirect the audio stream to an appropriate BT gateway based on the connection quality. Main contributions of UAAP are as follows:
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CP-Handoff for the LW-BT headset: The transmission of audio files will not be suspended even if the user uses a computing powerless client device, i.e., a LW-BT headset.
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Eliminating long baseband setup latency: Close to zero baseband handoff latency is achieved through the use of multiple basebands.
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Ubiquitous audio access: Users can listen to audio files anywhere in the UPnP home network with the Web Interfaces.
The remaining part of this paper is organized as follows. Related works are given in Section 2. The overview of Bluetooth handoff and its relevant issues are introduced in Section 3. The proposed CP-Handoff is given in Section 4. The UAAP system architecture is introduced in Section 5. The evaluation and performance results are given in Section 6. Finally, conclusion remarks are given in Section 7.
Section snippets
Related works
Many works have been done on the wireless audio streaming in the home network [5], [6]. Therefore, multimedia entertainment services can be in the home network over the UPnP platform [7], [8]. One selection of the wireless technologies for the home network is Bluetooth [9]. Bluetooth is intended to replace the cables connecting portable or fixed devices.
Bellavista et al. and Bilan [10], [11] introduced a platform for wirelessly streaming audio to mobile devices. Zeadally and Kumer [12], [13]
Issues of CP-handoff for bluetooth audio applications
The main limitations of the LW-BT headset for dealing with CP-handoff are discussed in this Section. Two main limitations for the LW-BT headset are (i) computation and (ii) communication.
Computation: The only one purpose for the LW-BT headset is to send/receive signal and play audio files from the BT gateway. The LW-BT headset doesn’t have the capability for computing other data. Several handoff control schemes require the mobile nodes to compute and decide when and how to perform handoff
Computing powerless handoff (CP-Handoff)
In this Section, the CP-Handoff for the LW-BT headset for high quality audio applications in the home network is introduced. The neighbor discovery algorithm, the CP-Handoff and Audio Packet Buffering and Perfecting are given in these subsections.
System architecture
Referring to Fig. 5, the main constitutions of UAAP are (1) the home gateway, (2) media servers, (3) BT gateways, and (4) the LW-BT headset.
The home gateway is responsible for managing audio files that are distributed in media servers in the home network. Media servers must register their audio files’ information to the home gateway. BT gateways are used for translating IP data to BT data. Audio files are streamed from media servers to LW-BT headset via the nearby BT gateway. Users can create a
Evaluation and performance
In the experiment, the BT gateway is implemented on Linux kernel 2.2.17 based on Bluez package [19]. The libupnp package is used for the UPnP module of the home gateway and media servers [20]. As depicted in Fig. 7, there are three BT gateways placed in three rooms. The three BT gateways are named as BTGW1, BTGW2 and BTGW3, respectively. BTGW1 and BTGW2 use the Bluetake BT009X dongle while BTGW3 uses the billionton GUBTCR41 dongle. The Bluetake BT009X supports Bluetooth USB Dongle Class 2,
Conclusion
In this paper, we have proposed the Computer Powerless Handoff control scheme (CP-Handoff) for devices without computing capability, such as the LW-BT headset in the digital home network, e.g., the UPnP home network. In the digital home network, audio files are distributed in media servers and are sent to the LW-BT headset via the BT gateway. The CP-Handoff is devised and dedicated for the LW-BT headset that is limited in (i) computation and (ii) communication. The proposed CP-Handoff includes
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The research is supported by the National Science Council of the Republic of China under Grant No. NSC 96-2219-E-006-008 and the Program of Top 100 Universities Advancement, Ministry of Education, Taiwan, Republic of China.