Introduction

What is TAISC?

The presence of wireless communication technologies is ever increasing and is expected to increase further due to the rise of Internet of Things (IoT) paradigm. Over the last two decades the speed at which these standards are being developed has grown significantly, resulting in a proliferation of wireless communication standards, each suitable for different application domains. Due to the shared nature of the limited ISM radio frequencies used in many wireless communication technologies, the use of an efficient medium access (MAC) protocol is crucial to ensure efficient wireless communications without collisions. Depending on the targeted application domain, wireless MAC protocols are typically optimized for low-power operation (e.g. ZigBee, Bluetooth low energy), low latency (e.g. wireless HART), high reliability (e.g. TSCH), high throughput (e.g. Wi-Fi) or a combination of the aforementioned requirements.

Due to increasingly diverse deployments and application loads, a sole one-size-fits-all MAC protocol can no longer meet the demands of many future wireless applications. As a result, a large number of MAC protocols have been proposed and evaluated in the scientific literature. However, in practice it is often not possible to select the most optimal MAC protocol for a specific application domain due to the following reasons: (i) wireless radio chips typically do not provide any support for updating, changing or replacing the MAC after deployment and (ii) since MAC implementations are typically written in low level, hardware specific code, it is very hard to reuse existing MAC protocols for different radio chips and/or technologies. To remedy this situation, this paper proposes the Time Annotated Instruction Set Computer (TAISC) framework for radio chips that solves both of these problems by (i) providing upgrade-ability of the MAC protocol and (ii) supporting reuse of MAC implementations through a cross-platform compilation phase. Several good reasons exist to support upgrade-ability and maintainability of MAC protocols. (i) MAC protocols from vendors often exhibit unwanted behavior or contain bugs that limit the performance of the wireless network. By supporting over-the-air upgrade capabilities of the radio firmware, these limitations can be corrected also after deployment. (ii) Wireless technologies are often replaced by new standards after just a few years, often building on top of the same physical layer (e.g.: ZigBee, Wireless HART, TSCH all use the IEEE 802.15.4 PHY layer). By supporting MAC upgradeability, users would be able to switch toward newer standards without having to replace all wireless radio boards. (iii) Wireless upgrade-ability of MAC protocols would allow users to cope with changing environmental conditions, for example by switching to a more interference robust MAC protocol. (iv) Similarly, over time, application requirements might change, for example when adding new devices to the network, it may be necessary to switch from CSMA/CA to TDMA based MAC protocols to cope with the increasing density of connected wireless devices.

Since MAC protocols are typically written in low level, hardware specific code, current MAC protocols cannot be reused for different radio chips and/or technologies. This is especially problematic for SME system integrators that target niche markets with specialized MAC protocols. Due to hardware obsolescence (i.e. the fact that radio chips from chip vendors typically have a life cycle of just a few years, far less than the life cycle of the end products they are used in), system integrators are frequently forced to integrate newer radio chip versions in their product. Most of the time their customdesigned MAC protocol cannot directly be reused on new radio chips, leading to a manpower and cost intensive redesign and testing phase that does not bring any added value to the end product. To remedy the above problems, TAISC introduces a crosscompilation process allowing MAC developers to design MAC protocols once, and then compile them for reuse on different radio chips. Although the MAC protocols are device-independent, TAISC allows the design of very efficient sleep schemes for energy constrained devices through the use of time-annotated instructions, thereby supporting time-critical behavior of the MAC protocol.

Documentation purpose

TAISC is used to implement MAC protocols for sensor devices in an easy manner. Following this documentation it should become clear how to:

  1. make adaptations to the existing MAC protocols;
  2. create your own custom TAISC MAC protocol;
  3. create an upper MAC for non-time critical behaviour in MAC protocols;
  4. make use of modules to update and monitor MAC level behaviour.