The handoff control scheme for computing powerless devices and its applications in the digital home network

Abstract

The evolution of wireless transmission technology enables users to have multimedia services anywhere in the digital home network. In this paper, we propose a handoff control scheme called Computing Powerless Handoff (CP-Handoff) for devices without computation capability, such as the light-weight Bluetooth (LW-BT) headset. The main concern of the CP-Handoff is that the client device doesn’t have the computation capability. The main function of the computing powerless client device is to send/receive signals and play the audio data. Thus, how to have the handoff control when a computing powerless client device is switched from one access point to another access point becomes a problem to be resolved. A typical example is in the BT wireless network environment. The LW-BT headset is dedicated for audio applications and doesn’t have extra computation capability. The CP-Handoff puts all handoff computation overhead on the master BT device, such that the LW-BT headset is unaware of the handoff. Based on the proposed CP-Handoff control scheme, a Ubiquitous Audio Access Platform (UAAP) is proposed and developed to allow users to access audio files using the LW-BT headset in the digital home network when they are roaming. The evaluation results show that the proposed CP-Handoff only needs 1.17 s to prepare the AVDTP session handoff and 0.38 s for the AVDTP session handoff. The transmission of audio packets to the LW-BT headset is only suspended for 0.38 s. The audio packet buffering scheme and retransmission mechanism ensure that the LW-BT headset can resume lost audio packets during handoff.

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:

• 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.

• Eliminating long baseband setup latency: Close to zero baseband handoff latency is achieved through the use of multiple basebands.

• 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.