## 1 Introduction  
Patient monitoring using biomedical sensors is a popular body area sensor network (WBASN) application that can to continuously monitor chronic and non-chronic diseases. WBASNs usually work in a star topology under the central control of a coordinator. A patient monitoring system is comprised of different sensors which measure physiological parameters including electrocardiography (ECG), electroencephalography (EEG), electromyography (EMG), accelerometry, gyroscopy, pulse oximeters, blood pressure, temperature, barometry and heart rate monitoring, etc. The sensors periodically collect data from the body and send it to a monitoring station through a coordinator node [1]. The periodic data from the sensors have different characteristics in the context of delivery delay and sensing rate. There are two basic reasons for the different characteristics of periodic data collected from various sensors; the first is collection from diverse physiological sources like blood pressure, ECG and temperature, etc., the second is the default behavior of the sensor. The efficient performance of WBASNs for patient monitoring systems requires a combined set of QoS including time bounded delays, reliability, appropriate throughput and energy efficiency. Besides the continuous monitoring of the periodic data from sensors, there is also exist some high priority data traffic that requires guaranteed services like ECG data, etc. Similarly, event-based emergency data may be generated at any time, e.g., when a sensor detects a stroke episode. The periodic data, high prioritized data and emergency data demand different sets of QoS [2; 3]. Therefore, the design of MAC protocols plays a vital role to provide appropriate communication services to the diverse sensors used in patient monitoring systems. Time-division multiple access (TDMA) and carrier sense multiple access with collision avoidance (CSMA/CA) are two basic MAC mechanisms used in WBASNs to support periodic and urgent traffic [4]. Usually, the CSMA/CA is considered to be appropriate for low, urgent, adaptive and scalable traffic patterns, whereas the TDMA is recommended for periodic traffic [5; 6; 7]. In this context, various hybrid MAC protocols are proposed [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29] based on IEEE 802.15.4 and IEEE 802.15.6 standards. These protocols can provide both channel access options i.e., CSMA/CA and TDMA. Usually, these protocols use time synchronization mechanisms to incorporate energy efficient mechanisms. The IEEE 802.15.4 defines a superframe structure containing a contention-free period (CFP) and a contention-access period (CAP). In the CAP, nodes deliver content for the channel using the slotted CSMA/CA, whereas CFP mode works in TDMA manner where the coordinator can assign maximum seven guaranteed time slots (GTS) to a request node. The WBASNs for patient monitoring systems deal with diverse bio-medical sensors which require services for periodic or urgent data. However, issues still exist with these hybrid protocols in terms of provision of a combined set of QoS including limited delay, reliability, appropriate throughput and efficient energy utilization for patient monitoring systems. The issues include random selection of backoff exponent BE without considering network conditions, MAC unreliability problems, lack of dynamic adaptive capabilities, unfair under saturation conditions, superframe duration selection, traffic priorities issues and the limited number of GTS slots etc. Table 1 provides the requirements of communication analysis for different bio-medical sensor devices. In this paper, a different approach is used to address the above issues and to optimize the performance of existing hybrid MAC protocols for patient monitoring systems. A frame aggregation mechanism is proposed at the MAC layer which will send multiple MAC frames under the single PHY header within a single successful channel access. This paper implements this idea for IEEE 802.15.4.